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The collapse of global cooperation and a failure of international solidarity have led to many low-income and middle-income countries being denied access to molecular diagnostics in the COVID-19 pandemic response. Yet the scarcity of knowledge on the dynamics of the immune response to infection has led to hesitation on recommending the use of rapid immunodiagnostic tests, even though rapid serology tests are commercially available and scalable. On the basis of our knowledge and understanding of viral infectivity and host response, we urge countries without the capacity to do molecular testing at scale to research the use of serology tests to triage symptomatic patients in community settings, to test contacts of confirmed cases, and in situational analysis and surveillance. The WHO R&D Blue Print expert group identified eight priorities for research and development, of which the highest is to mobilise research on rapid point-of-care diagnostics for use at the community level. This research should inform control programmes of the required performance and utility of rapid serology tests, which, when applied specifically for appropriate public health measures to then be put in place, can make a huge difference.
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remains active. Published online July 17, 2020
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Lancet Infect Dis 2020
Published Online
July 17, 2020
Department of Clinical
Research, London School of
Hygiene & Tropical Medicine,
London, UK
(Prof R W Peeling PhD,
C J Wedderburn MBChB,
N Fongwen MD,
Prof D L Heymann MD);
Neuroscience Institute and
Department of Paediatrics and
Child Health, University of
Cape Town, Cape Town,
South Africa (C J Wedderburn);
Universidad Peruana Cayetano
Heredia, Lima, Peru
(Prof P J Garcia MD); Global
Health Impact Group, Atlanta,
GA, USA (D Boeras PhD); Africa
Centres for Disease Control and
Prevention, Addis Ababa,
Ethiopia (J Nkengasong PhD);
Institut Pasteur Dakar, Dakar,
Senegal (A Sall PhD); and
Federal University of
Rio de Janeiro, Rio de Janeiro,
Brazil (Prof A Tanuri MD)
Correspondence to:
Prof Rosanna W Peeling,
Department of Clinical Research,
London School of Hygiene &
Tropical Medicine,
London WC1E 7HT, UK
Serology testing in the COVID-19 pandemic response
Rosanna W Peeling, Catherine J Wedderburn, Patricia J Garcia, Debrah Boeras, Noah Fongwen, John Nkengasong, Amadou Sall, Amilcar Tanuri,
David L Heymann
The collapse of global cooperation and a failure of international solidarity have led to many low-income and middle-
income countries being denied access to molecular diagnostics in the COVID-19 pandemic response. Yet the scarcity
of knowledge on the dynamics of the immune response to infection has led to hesitation on recommending the use
of rapid immunodiagnostic tests, even though rapid serology tests are commercially available and scalable. On the
basis of our knowledge and understanding of viral infectivity and host response, we urge countries without the
capacity to do molecular testing at scale to research the use of serology tests to triage symptomatic patients in
community settings, to test contacts of confirmed cases, and in situational analysis and surveillance. The WHO R&D
Blue Print expert group identified eight priorities for research and development, of which the highest is to mobilise
research on rapid point-of-care diagnostics for use at the community level. This research should inform control
programmes of the required performance and utility of rapid serology tests, which, when applied specifically for
appropriate public health measures to then be put in place, can make a huge dierence.
Diagnostics: the weak link in the COVID-19
pandemic response
The COVID-19 pandemic, now only a few months old,1,2
has brought into sharp focus inequalities within and
among countries. John Nkengasong, Director of the
Africa Centres for Disease Control and Prevention,
reported that “the collapse of global cooperation and a
failure of international solidarity have shoved Africa out
of the diagnostics market”.3 Sadly, the same is true of
many other low-income and middle-income countries
(LMICs) outside Africa.
Why are diagnostics important? In any epidemic
response, diagnostic testing plays a crucial role and this
pandemic is no exception. Because early clinical
presentations of infected patients are non-specific,
testing is needed to confirm the diagnosis of COVID-19
in symptomatic patients, as soon as possible, so
that these patients can be appropriately isolated and
clinically managed.1,4,5 Diagnostic testing is also needed
for individuals who have come into contact with
someone with confirmed COVID-19. Some testing
strategies examine only contacts who have symptoms
or develop illness of any kind during the 14-day period
after contact. Other strategies examine all contacts
when identified, regardless of whether they have any
symptoms. Studies have shown that a large number of
infected individuals might have no symptoms at
all, and there is concern that these individuals are
still able to shed the virus and transmit infection
through saliva droplets as they speak.4–9 Tracking all
contacts of confirmed cases and testing them for severe
acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
is key to successful pandemic control. Diagnostics are
also needed to support rapid serosurveys that establish
whether and to what extent SARS-CoV-2 has circulated
in a community, and sur veillance systems, such as that
for influenza-like illness, that monitor disease trends
over time. Diagnostics can also be used to identify at-
risk populations and assess the eectiveness of control
Tedros Adhanom Ghebreyesus, Director-General of
WHO, urged countries to implement a comprehensive
package of measures to find, isolate, test, and treat every
case, and trace every contact. Goodwill between countries
has already been shown through the publishing of the
SARS-CoV-2 genetic sequence and shared laboratory
protocols to detect the virus.10 However, as these molecular
assays require sophisticated labora tory facilities, countries
with insucient infrastructure quickly accumulate a
backlog of testing. The rapid spread of COVID-19 around
the world has led to a global shortage of reagents and
supplies needed for testing. Point-of-care molecular
assays for SARS-CoV-2 detection are now available to
enable community-based testing for COVID-19 in LMICs.
Unfortunately, the production of these test cartridges
takes time and, again, global demand has outstripped
supply, leaving LMICs struggling for access.
Test, test, test
In March, 2020, WHO urged member states to “test, test,
test”.11 Widespread testing can help countries to map the
true extent of the outbreak, including identifying hot
spots and at-risk populations, and monitor the rate at
which the epidemic is spreading. However, most LMICs
find that molecular testing, including point-of-care
testing, is neither scalable nor aordable on a large scale.
Relying solely on centralised testing puts countries at
risk of having nothing to use. What diagnostic alternatives
are available to support decentralised testing that would
allow countries to mount an adequate response to the
Rapid antigen detection tests that are simple to do at
point of care and can give results in less than 30 min
would be viable alternatives to molecular testing for
confirming COVID-19 cases, enabling appropriate case
management, and guiding public health measures, such
as quarantine or self-isolation. However, although scaling
up rapid antigen testing oers an eective means of
triaging symptomatic individuals in community settings,
early evaluations of rapid antigen detection tests show
2 Published online July 17, 2020
Personal View
suboptimal sensitivity for these tests to be recommended
for clinical diagnosis or triage.12
Rapid antibody detection lateral flow tests are also simple
to use, generally requiring a few drops of whole blood
from a finger prick placed onto the test strip with no
processing needed. These tests take 15–20 min to do with
minimal training and can be done at the point of care as
most do not require any equipment. Rapid antibody testing
is an attractive option for scaling up testing but only if
these tests show satisfactory performance for a clearly
specified use.
SARS-CoV-2 infectivity and immune response
The detection of SARS-CoV-2 infection and immune
response has been described in relation to dierent
diagnostic tests.13 In this section, we summarise the
evidence from studies to date.
Viral infectivity
Studies have shown that SARS-CoV-2 RNA can be
detected 2–3 days before onset of symptoms and can
remain detectable up to 25–50 days after the onset
of symptoms, particularly in patients who remain
symptomatic for an extended period.7,14,15 SARS-CoV-2
RNA can be detected for longer in respiratory samples
from patients with severe disease than in samples from
patients with mild illness.16 Viral RNA concentrations
peak within the first 5 days after onset of symptoms and
decrease slowly with rising antibody concentrations.7,17,18
However, RNA clearance is not always associated with
rising antibody concentrations, particularly in patients
who were critically ill.6,18 An important question for the
potential for spread of COVID-19 is whether individuals
who are RNA-positive are shedding infectious virus. A
small study in nine patients found that viral replication
stopped 5–7 days after onset of symptoms but patients
remained RNA-positive for 1–2 weeks after this point.6
Hence, there remains some uncertainty as to whether a
patient who is RNA-positive is shedding live virus or not.
Immune response to COVID-19 disease
Maturation of the immune response typically takes
40 days with variations in the dynamics of the antibody
response depending on disease severity and other factors
still to be discovered. In most studies of laboratory-
confirmed COVID-19 cases, IgM antibodies start to be
detectable around 5–10 days after onset of symptoms and
rise rapidly.14,18–21 IgG antibody concentrations follow the
IgM response closely. Seroconversion is typically within
the first 3 weeks with the mean time for seroconversion
being 9–11 days after onset of symptoms for total antibody,
10–12 days for IgM, and 12–14 days for IgG.14,18,19,22
COVID-19 antibody response: pathogenic or protective?
Antibodies against the receptor-binding domain of the
spike protein and the nucleocapsid protein have been
associated with neutralising activity.14,23,24 Neutralising
anti bodies to these domains can be detected approximately
7 days after onset of symptoms and rise steeply over the
next 2 weeks.23,24 Several studies showed that patients
can remain RNA-positive despite high concentrations of
IgM and IgG antibodies against the nucleocapsid protein
and the receptor-binding domain of the spike protein.18
Whether the presence of neutralising antibodies trans-
lates into protective immunity in patients with COVID-19
is unclear. Some researchers speculate that antibodies can
enhance infectivity as higher antibody concentrations
have been observed in patients with severe disease than in
those with mild disease.18,25 In one study (n=222), a greater
proportion of patients with high IgG concentrations had
severe disease than did those with low IgG concentrations
(52% vs 32%, p=0·008).26 The role of antibody response in
the pathogenesis of COVID-19 remains unclear pending
further studies.
Ideal testing strategies versus reality
WHO and the Pan American Health Organization have
stated that they do not currently recommend the use of
immunodiagnostic tests except in research settings,27,28
because of scarce information on test performance and
appropriate use when immunity to COVID-19 is not well
under stood. However, many countries are struggling to
scale up testing to implement the key strategies of diag-
nosing all symptomatic patients and tracing all contacts.
Delays in confirming COVID-19 cases allow continued
transmission within communities and can result in failure
to contain the pandemic despite other mea sures such as
physical distancing and travel restrictions.
How can countries move forward?
Countries are assessing all available testing options to
address their range of needs. In settings where challenges
with molecular testing exist or access to laboratories
is scarce, rapid serology tests oer a needed additional
option. A rapid serology test with good performance chara-
cter istics is extremely important to avoid missing true
cases of COVID-19 and imposing unnecessary quaran tine
for people with false-positive results due to cross-reactivity
with seasonal coronaviruses. Studies have shown more
anti body cross-reactivity between the nucleo capsid
proteins of SARS-CoV-2 and common corona viruses than
between their spike proteins.20,22 Tests that use the spike
protein or fragments of the spike protein as targets might
have the least amount of cross-reactivity with common
coronaviruses, on the basis of sequence analysis.22 Clear
articulation of the benefits and limitations of serology tests
will hopefully incentivise manufacturers to improve
When is serology testing recommended?
Rapid triage of symptomatic individuals in community
Where there is little or no access to molecular testing,
rapid serology tests provide a means to quickly triage Published online July 17, 2020
Personal View
suspected cases of COVID-19, provided the test is
highly specific for the disease. A positive result for IgM
in symptomatic patients fulfilling the COVID-19 case
definition is strongly suggestive of SARS-CoV-2 infection.
This approach is probably most eective in individuals
5–10 days after symptom onset.
In Peru, public health facilities for molecular testing are
sparse and only 500 beds in intensive care units exist for a
population of 32 million. The Ministry of Health has set up
a hotline and website for individuals who have symptoms
to be interviewed by a health professional for possible
follow-up, prioritising the visits according to age, risk
factors, and severity of symptoms. A testing team visits the
individual at home to do the rapid anti body test. Individuals
who are IgM and IgG positive and have mild symptoms
are quarantined, whereas people who need critical care are
referred to hospital. All contacts are also tested with the
rapid serology test. Anyone who tests negative in the
antibody test has a swab collected for molecular testing.
As of May 2, 2020, 355 604 people had been triaged in
Peru with 42 534 testing positive, 26 362 of whom were
found to be positive by use of a rapid test.30 This approach
has allowed a large number of sympto matic individuals
and contacts to be rapidly tested in the community,
relieving the backlog, reducing waiting time for molecular
testing, and preventing the health-care system from being
Experience in China has also shown that, in sympto-
matic patients, the use of IgM tests or total antibody tests
can increase the sensitivity of COVID-19 case detection.18
Further research should explore the performance and
utility of rapid antigen-IgM and antigen-IgG combo tests
and the timing of testing. In individuals who test negative
for IgG, research should also explore, if resources allow,
the value of doing a follow-up antibody test 10–14 days
later to document a definitive diagnosis through sero-
Testing all contacts of people with confirmed COVID-19
Studies have shown that a large number of infected
individuals could have only mild symptoms or no
symptoms at all, but they can still transmit infection, with
as much as 44% of infections being transmitted by pre-
symptomatic individuals.6,7,9 Experience from Singapore
shows that tracking down all contacts of people with
confirmed COVID-19, testing them for evidence of
infection, regardless of symptoms, and putting those
contacts who test positive into isolation is an urgent
priority for interrupting the chain of transmission and
containing the epidemic.31–33 This approach is particularly
important in the early stages when there are only sporadic
or clusters of cases, or for countries coming down from
the peak to continue to reduce the extent of infection
in the community. Only individuals who test negative
should have a throat swab collected for molecular testing,
which will reduce the strain on laboratories doing
these tests.
Situational analysis and surveillance
In countries that have set up syndromic surveillance, such
as surveillance for influenza-like illness or severe acute
respiratory infections, and where blood or throat swabs
are routinely collected at these sentinel sites, collected
samples can be tested for COVID-19 with molecular,
antigen, or serology tests, either alone or in combination.
If any of these samples are positive, it means COVID-19
has been circulating in the community. Where serial
samples are available, it might be possible to date when
COVID-19 established itself in a community or country.
In general, antibody tests can be used to establish
the true extent of an outbreak, map its geographical
distribution, and identify hotspots and populations that
are particularly at risk. This information can in turn
be used to inform public health measures and control
strategies. In this case, researchers need to stick to the
same serology test and test sentinel populations
repeatedly, avoiding the variation in sensitivity between
dierent rapid tests.
When is serology testing not recommended?
Testing the general population
The use of serology tests for population surveys is not
recommended in low prevalence settings as this approach
will probably result in more false-positive than true-
positive results, even if a test with high specificity is used.
For example, if the prevalence of infection is 1% in the
general population, a test with 98% specificity will
identify two false-positive results for every true positive
result. These results could lead to a false sense of security
regarding the extent of immunity in the population and
premature easing of public health measures on the basis
of misleading disease estimates.
Patients at an early stage in the disease course, or
asympto matic or paucisymptomatic patients, might
have low antibody concentrations that could give false-
negative results. Patients’ disease stage and severity are
important points to consider, along with the population
being tested. The estimated level of risk can be considered
before using a serology test, because of the changing false-
positive rate or low positive predictive value across dierent
populations. Among the groups with the highest risk of
the disease are symptomatic patients with clinical presen-
tation of COVID-19, patients with other respiratory
symptoms, contacts of confirmed cases, and health-care
workers in settings with little personal protective equip-
ment. We suggest countries consider risk levels before
using serology tests and creating public health guidance.
Scaling up testing, particularly at the community level,
allows for better estimates of risks, which in turn allows
more eective public health measures to be put into place
than would be otherwise.
Testing to allow health-care workers to return to work
In a pandemic, countries must strive to maintain a
robust health-care workforce. Key workers who develop
4 Published online July 17, 2020
Personal View
symptoms should be prioritised for molecular testing
and receive care if infected. On recovery, should a
serology test be used to decide when they can safely
return to work? This strategy is based on the assumption
that antibodies confer protective immunity.
Although antibodies against the receptor-binding
domain of the spike protein and the nucleocapsid
protein have been correlated with neutralising activity,14,23,24
the development and duration of immunity has not yet
been established.34,35 Although it is tempting to speculate
that serology tests based on the detection of neutralising
antibodies can be used as markers of protective immunity,
and people who test positive can get a so-called immunity
passport to return to work, studies have shown that a
significant proportion of patients remain RNA-positive
despite high concen trations of antibodies against the
receptor-binding domain of the spike protein and the
nucleocapsid protein.6,15,18,20,21 Wang and colleagues36 found
that elevated serum IgM concentrations are correlated
with poor outcomes in patients with COVID-19
pneumonia, and Tan and colleagues21 found that high
concentrations of IgG antibodies were correlated with
severe disease outcomes. Hence a substantial IgM or IgG
response is not necessarily a surrogate marker of
protective immunity. To date, insucient evidence exists
to recommend the use of serology testing for health-care
workers to return to work. A negative molecular test
remains the safest option to establish whether health-care
workers can work again safely.
A policy brief by the World Bank suggested that serology
testing could potentially have a high net benefit if it can
allow dilution of restrictions for essential workers to return
to work and revive essential segments of the economy.37
The type of tests that can be used for immunity passports
remains unclear. A better understanding of the interaction
between infection and immune response dynamics is
needed before these passports can be considered.
Testing to discharge patients from hospitals
Hospital beds are often in short supply. The recom-
mended criteria for hospital discharge are two negative
molecular tests over several days. However, molecular
testing is often scarce or unavailable. Can serology
tests be used for discharging recovered patients when
molecular testing is not available?
As patients can remain positive for viral RNA despite
rising concentrations of antibodies against the nucleo-
capsid protein and receptor-binding domain of the spike
protein, which are correlated with neutralising activities,
antibody tests cannot be used in the place of molecular
tests to confirm that the patient is virus-free or at least no
longer shedding live virus.
The events over the past few months have taught us that
this pandemic is caused by an extraordinary pathogen
that requires extraordinary measures to combat its
spread and end the pandemic. The latest finding that as
much as 44% of COVID-19 transmission happens before
index cases become symptomatic7 means that a great
deal still needs to be learnt about this novel pathogen and
its spread through a population. The paucity of
knowledge on the dynamics of the immune response to
infection has led to much hesitation on recommending
the use of rapid immuno diagnostic tests, particularly
serology tests.
On the basis of our current knowledge and understanding
of viral infectivity and host response, we urge countries
with restricted capacity for molecular testing to embark on
research into the use of serology tests in triaging symp-
tomatic patients in community settings, testing contacts of
confirmed cases, and in situational analysis and
surveillance. Rapid and scalable tests are needed to deal
with this pandemic. Rapid serology tests, applied in the
right situation for appropriate public health measures to
be put into place, can make a huge dierence. On
Feb 10, 2020, leading health experts from around the world
identified eight research and development priorities at the
WHO R&D Blue Print meeting in Geneva, Switzerland, of
which the top priority was to “mobilize research on rapid
point of care diagnostics for use at the community level”.38
In line with this decision, research on the use of rapid
serology tests to inform control programmes of their
required performance and utility is an urgent priority in
the COVID-19 pandemic response.
RWP wrote the first draft of the manuscript. All authors contributed to
the manuscript conception and supported manuscript revisions.
Declaration of interests
We declare no competing interests.
We thank Sergio Carmona and Jilian Sacks of the Foundation for
Innovative New Diagnostics for helpful discussions.
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... Cohort studies associated with disease surveillance are essential for understanding pathogens' circulation, surrogates of protection, disease burden, and demand for health services, especially in poor communities in LMIC. By following individuals over time, cohorts provide granular data for monitoring disease trends 5,6 and the long-term impacts of the pandemic. Prospective studies may fill knowledge gaps regarding the burden of disease and risk factors in a vulnerable population 7 . ...
Background: Socially vulnerable populations were vastly affected by the COVID-19 pandemic. The pandemic significantly impacted Brazil, pressuring its healthcare system for several months, with high mortality rates, even among the youngest population. Cohort studies combining disease surveillance are essential for understanding virus circulation in the community, surrogates of protection, vaccine effectiveness, and demand for health resources. Methods: Here, we present the protocol for a community-based prospective cohort study in the largest complex of favelas (slums) in Rio de Janeiro, Brazil (Complexo da Maré). The study participants are residents initially recruited during a massive vaccination campaign in the community. Five waves of data collection at approximately six-month intervals were planned. The first two waves have been completed at the time of writing this study protocol, and the third is underway. The protocol comprises interviews, blood sampling, and records linkage with secondary data to enrich the profiles of cohort participants and community information. We will describe COVID-19 seroprevalence, socio-demographic characteristics, and the burden of COVID-19, followed by estimating the association of socioeconomic factors and the burden of disease with seroprevalence. Discussion: The primary aims of the study are to assess COVID-19 clinical, epidemiological and genomic profiles and outcomes in residents from Maré, including vaccine effectiveness, surrogates of immune protection, virus transmission in households, and the overall burden of the pandemic.
... Another caveat is that in COVID-19, the kinetics of the neutralizing antibody response is typical of an acute viral infection, with declining neutralizing antibody titers observed after an initial peak and a magnitude of this peak that is dependent on disease severity [15]. Furthermore, serological tests are often difficult to administer and costly [16][17][18]. ...
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Epidemics and pandemics require an early estimate of the cumulative infection prevalence, sometimes referred to as the infection "Iceberg," whose tip are the known cases. Accurate early estimates support better disease monitoring, more accurate estimation of infection fatality rate, and an assessment of the risks from asymptomatic individuals. We find the Pivot group, the population sub-group with the highest probability of being detected and confirmed as positively infected. We differentiate infection susceptibility, assumed to be almost uniform across all population sub-groups at this early stage, from the probability of being confirmed positive. The latter is often related to the likelihood of developing symptoms and complications, which differs between sub-groups (e.g., by age, in the case of the COVID-19 pandemic). A key assumption in our method is the almost-random subgroup infection assumption: The risk of initial infection is either almost uniform across all population sub-groups or not higher in the Pivot sub-group. We then present an algorithm that, using the lift value of the pivot sub-group, finds a lower bound for the cumulative infection prevalence in the population, that is, gives a lower bound on the size of the entire infection "Iceberg." We demonstrate our method by applying it to the case of the COVID-19 pandemic. We use UK and Spain serological surveys of COVID-19 in its first year to demonstrate that the data are consistent with our key assumption, at least for the chosen pivot sub-group. Overall, we applied our methods to nine countries or large regions whose data, mainly during the early COVID-19 pandemic phase, were available: Spain, the UK at two different time points, New York State, New York City, Italy, Norway, Sweden, Belgium, and Israel. We established an estimate of the lower bound of the cumulative infection prevalence for each of them. We have also computed the corresponding upper bounds on the infection fatality rates in each country or region. Using our methodology, we have demonstrated that estimating a lower bound for an epidemic's infection prevalence at its early phase is feasible and that the assumptions underlying that estimate are valid. Our methodology is especially helpful when serological data are not yet available to gain an initial assessment on the prevalence scale, and more so for pandemics with an asymptomatic transmission, as is the case with Covid-19.
... Serological tests are simpler to develop, more practical, and provide faster results [18]. Advancements in serological tests have marked immunoglobins, e.g., IgM, IgG, and IgA, etc., as important biomarker tools [19,20]. Moreover, our literature review identifies positive results with IgG and IgM tests either exclusively or combined [21]. ...
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Human antibodies are produced due to the activation of immune system components upon exposure to an external agent or antigen. Human antibody G, or immunoglobin G (IgG), accounts for 75% of total serum antibody content. IgG controls several infections by eradicating disease-causing pathogens from the body through complementary interactions with toxins. Additionally, IgG is an important diagnostic tool for certain pathological conditions, such as autoimmune hepatitis, hepatitis B virus (HBV), chickenpox and MMR (measles, mumps, and rubella), and coronavirus-induced disease 19 (COVID-19). As an important biomarker, IgG has sparked interest in conducting research to produce robust, sensitive, selective, and economical biosensors for its detection. To date, researchers have used different strategies and explored various materials from macro- to nanoscale to be used in IgG biosensing. In this review, emerging biosensors for IgG detection have been reviewed along with their detection limits, especially electrochemical biosensors that, when coupled with nanomaterials, can help to achieve the characteristics of a reliable IgG biosensor. Furthermore, this review can assist scientists in developing strategies for future research not only for IgG biosensors but also for the development of other biosensing systems for diverse targets.
... A particularly important role is played by polymer microparticles conjugated with appropriate immunoglobulins or antigens, referred to as immunolatexes. Beginning from the pioneering work of Plotz 1956 [11], who developed the first latex agglutination assay for rheumatoid arthritis, such particles are used in a plethora of other tests against various bacterial infections, most often E. coli, Salmonella [12][13][14][15][16], viral infections such as HIV and, recently, SARS-Cov 2 [17][18][19][20]. The extensive application range of such tests is the effect of their simplicity and short execution time, of the order of minutes [21], which is particularly important for points of care testing. ...
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Physicochemical properties of immunolatex, prepared by incubation of negatively charged polystyrene microparticles with polyclonal rabbit IgGs, were determined by a variety of experimental techniques. These comprised dynamic light scattering (DLS), laser Doppler velocimetry (LDV) and atomic force microscopy (AFM). The particle diffusion coefficient, the hydrodynamic diameter, the electrophoretic mobility, the zeta potential and the suspension stability were determined as a function of pH for different ionic strengths. The deposition of the immunolatex on bare and polyallylamine (PAH) functionalized mica was investigated using the microfluidic oblique impinging-jet cell, with an in situ, real-time image analysis module. The particle deposition kinetics was acquired by a direct particle enumeration procedure. The measurements enabled us to determine the range of pH where the specific deposition of the immunolatex on these substrates was absent. We argue that the obtained results have practical significance for conducting efficient flow immunoassays governed by specific antigen/antibody interactions.
... In contrast, IgG is detectable after seven days and increases later (after ~14 days), providing a long-term humoral response. IgG levels are typically higher in severe rather than in mild cases, as well as in critical COVID-19 cases [25]. In other studies on patients with COVID-19, [24,26]. ...
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The recent identification of the involvement of the immune system response in the severity and mortality of acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection highlights the importance of cytokines and chemokines as important factors in the clinical outcomes of COVID-19. However, the impact and roles of the BAFF/APRIL cytokine system, homeostatic chemokines (CXCL12, CXCL13, CCL19, and CCL21), as well as Toll-like receptor (TLR)-3/4 in COVID-19, have not been investigated. We sought to assess the expression levels and roles of TLR3/4, BAFF, APRIL, IFN-β, homeostatic chemokines (CXCL12, CXCL13, CCL19, and CCL21), SARS-CoV-2 IgG and IgM antibodies in patients with critical (ICU) and non-ICU (mild) COVID-19 and their association with mortality and disease severity. Significant high levels of TLR-4 mRNA, IFN-β, APRIL, CXCL13, and IgM and IgG antibodies were observed in ICU patients with severe COVID-19 compared to non-ICU COVID-19 patients and healthy controls. On the other hand, BAFF and CCL21 expression were significantly upregulated in non-ICU patients with COVID-19 compared with that in critical COVID-19 patients. The two groups did not differ in TLR-3, CXCL12, and CCL19 levels. Our findings show high expression levels of some inflammatory chemokines in ICU patients with COVID-19. These findings highlight the potential utility of chemokine antagonists as an immune-based treatment for the severe form of COVID-19. We also believe that selective targeting of TLR/spike protein interactions might lead to the development of a new COVID-19 therapy.
... measuring immunogenicity and estimating level of protection) (Krajewski et al., 2020), and epidemiological investigation (e.g. tracing the transmission in a community and estimating seroprevalence to quantify the level of herd immunity) (Watson et al. 2020;Peeling et al., 2020;Lisboa Bastos et al., 2020). Numerous products with different platforms have been developed, including lateral flow immunochromatography, enzyme-linked immunosorbent assay (ELISA), chemiluminescent assays, and neutralization assays (Theel et al., 2020;Galipeau et al., 2020). ...
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Accurate immunoassays with a good correlation to neutralizing antibodies are required to support SARS-CoV-2 diagnosis, management, vaccine deployment, and epidemiological investigation. We conducted a study to evaluate the performance and correlation of the surrogate virus neutralization test (sVNT) and other commercial immunoassays. We tested 107 sera of COVID-19 confirmed cases from three different time points, 58 confirmed non-COVID-19 sera, and 52 sera collected before the pandemic with two sVNTs, seven chemiluminescent assays, and one fluorescein assay. All assays achieved excellent sensitivity (95% to 100%, ≥15 days after onset of illness), specificity (95.5% to 100%), and showed moderate to high correlation with GenScript sVNT (r=0.58 to r=0.98), except Roche total antibodies (r=0.48). Vazyme sVNT and Siemens total antibodies showed the highest correlation with GenScript sVNT (r=0.98 and 0.88, respectively). Median indexes that may be used to estimate sera with the highest ability to inhibit SARS-CoV-2 and ACE-2 receptor attachment (GenScript sVNT inhibition 90%-100%) were 6.9 S/C (Abbott IgG), 161.9 COI (FRENDTM IgG), 16.8 AU/ml (Snibe IgG), 40.1 S/CO (Beckman IgG), 281.9 U/ml (Mindray IgG), 712.2 U/ml (Mindray total antibodies), >10 index (Siemens total antibodies), and 95.3% inhibition (Vazyme sVNT). All ten commercial COVID-19 serology assays, with different targeting antigens, demonstrated a reliable performance, supporting the utility of those assays in clinical and research settings. However, further studies using more samples are needed to refine the results of evaluating the performances of these marketed serological assays. Reliable serological assays would be useful for clinicians, researchers and epidemiologists in confirming SARS-CoV-2 infections, observing SARS-CoV-2 transmission, and immune response post infection and vaccination, leading to better management and control of the disease.
... Some chemical sensors have been widely used outside of specialized professions and can be purchased as commercial products, such as pH-dye litmus paper [5], blood sugar monitors [6], and pregnancy tests [7]. One of the sensor systems that is likely to remain most important in this decade is the COVID-19 rapid antigen test [8,9]. The main reason such sensors have become so popular is that they are cheap, disposable, and easy to use. ...
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Most organic solvents are colorless liquids, usually stored in sealed containers. In many cases, their identification depends on the appropriate description on the container to prevent mishandling or mixing with other materials. Although modern laboratories rely heavily on identification technologies, such as digitized inventories and spectroscopic methods (e.g., NMR or FTIR), there may be situations where these cannot be used due to technical failure, lack of equipment, or time. An example of a portable and cost-effective solution to this problem is an electrochemical sensor. However, these are often limited to electrochemical impedance spectroscopy (EIS) or voltammetry methods. To address this problem, we present a novel modular electrochemical sensor for solvent identification that can be used with either an EIS-enabled potentiostat/galvanostat or a simple multimeter. A novel method of fabricating and using a sensor consisting of a thin-film coating of an organic substance on a stainless-steel electrode substrate is presented. The differences in the solubility of the thin film in different solvents are used to distinguish between common organic solvents such as water, ethanol, and tetrahydrofuran.
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Background: COVID-19 pandemic caused by extended variants of SARS-CoV-2 has infected more than 350 million people, resulting in over 5.5 million deaths globally. However, the actual burden of the pandemic in Africa, particularly among children, remains largely unknown. We aimed to assess the seroepidemiological changes of SARS-CoV-2 infection after school reopening among school children in Oromia, Ethiopia. Methods: A prospective cohort study involving students aged 10 years and older were used. A serological survey was performed twice, at school reopening in December 2020 and four months later in April 2021. Participants were selected from 60 schools located in 15 COVID-19 hotspot districts in Oromia Region. Serology tests were performed by Elecsys anti-SARS-CoV-2 nucleocapsid assay. Data were collected using CSentry CSProData Entry 7.2.1 and exported to STATA version 14.2 for data cleaning and analysis. Results: A total of 1884 students were recruited at baseline, and 1271 completed the follow-up. SARS-CoV-2 seroprevalence almost doubled in four months from 25.7% at baseline to 46.3% in the second round, with a corresponding seroincidence of 1910 per 100,000 person-week. Seroincidence was found to be higher among secondary school students (grade 9-12) compared to primary school students (grade 4-8) (RR = 1.6, 95% CI 1.21-2.22) and among those with large family size (> = 5) than those with a family size of <3 (RR = 2.1, 95% CI 1.09-4.17). The increase in SARS-CoV-2 seroprevalence among the students corresponded with Ethiopia's second wave of the COVID-19 outbreak. Conclusion: SARS-CoV-2 seroprevalence among students in hotspot districts of the Oromia Region was high even at baseline and almost doubled within four months of school recommencement. The high seroincidence coincided with the second wave of the COVID-19 outbreak in Ethiopia, indicating a possible contribution to school opening for the new outbreak wave.
Lateral flow immunoassays (LFIA) for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies are used for population surveillance and potentially individual risk assessment. The performance of the SureScreen Diagnostics LFIA targeting the spike protein was evaluated in comparison with 3 automated assays (Abbott Alinity-i SARS-CoV-2 IgG, DiaSorin Liaison® SARS-CoV-2 S1/S2 IgG, Wantai SARS-CoV-2 Ab ELISA). We assessed sensitivity using 110 serum samples from PCR confirmed COVID-19 infected patients. Specificity was evaluated using 120 prepandemic samples, including potential cross-reactive antibodies samples. Sensitivity ranged between 93.3% and 98.7% on samples collected >14 days postsymptom onset. All assays achieved a specificity >98%. Moreover, its performance seems not to be affected by Alpha, Beta or Delta variants over a wide range of antibody titers. The latter showed a very good agreement with the Wantai and the Abbott assays and a substantial agreement with the DiaSorin assay. Our data demonstrate the good clinical performance of the SureScreen Diagnostics LFIA for SARS-CoV-2 seroprevalence screening.
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Introduction: A recently emerging respiratory disease named coronavirus disease 2019 (COVID-19) has quickly spread across the world. This disease is initiated by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and uncontrolled cytokine storm, but it remains unknown as to whether a robust antibody response is related to clinical deterioration and poor outcome in COVID-19 patients. Methods: Anti-SARS-CoV-2 IgG and IgM antibodies were determined by chemiluminescence analysis (CLIA) in COVID-19 patients at a single center in Wuhan. Median IgG and IgM levels in acute and convalescent-phase sera (within 35 days) for all included patients were calculated and compared between severe and non-severe patients. Immune response phenotyping based on the late IgG levels and neutrophil-to-lymphocyte ratio (NLR) was characterized to stratified patients into different disease severities and outcomes. Results: A total of 222 patients were included in this study. IgG was first detected on day 4 of illness, and its peak levels occurred in the fourth week. Severe cases were more frequently found in patients with high IgG levels, compared to those with low IgG levels (51.8 vs. 32.3%; p = 0.008). Severity rates for patients with NLRhiIgGhi, NLRhiIgGlo, NLRloIgGhi, and NLRloIgGlo phenotype were 72.3, 48.5, 33.3, and 15.6%, respectively (p < 0.0001). Furthermore, severe patients with NLRhiIgGhi, NLRhiIgGlo had higher inflammatory cytokines levels including IL-2, IL-6 and IL-10, and decreased CD4+ T cell count compared to those with NLRloIgGlo phenotype (p < 0.05). Recovery rates for severe patients with NLRhiIgGhi, NLRhiIgGlo, NLRloIgGhi, and NLRloIgGlo phenotype were 58.8% (20/34), 68.8% (11/16), 80.0% (4/5), and 100% (12/12), respectively (p = 0.0592). Dead cases only occurred in NLRhiIgGhi and NLRhiIgGlo phenotypes. Conclusions: COVID-19 severity is associated with increased IgG response, and an immune response phenotyping based on the late IgG response and NLR could act as a simple complementary tool to discriminate between severe and non-severe COVID-19 patients, and further predict their clinical outcome.
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Background Timely diagnosis of SARS-CoV-2 infection is a prerequisite for treatment and prevention. The serology characteristics and complement diagnosis value of the antibody test to RNA test need to be demonstrated. Method Serial sera of 80 patients with PCR-confirmed COVID-19 were collected at the First Affiliated Hospital of Zhejiang University, China. Total antibody (Ab), IgM and IgG antibodies against SARS-CoV-2 were detected, and the antibody dynamics during the infection were described. Results The seroconversion rates for Ab, IgM and IgG were 98.8%, 93.8% and 93.8%, respectively. The first detectible serology marker was Ab, followed by IgM and IgG, with a median seroconversion time of 15, 18 and 20 days post exposure (d.p.e) or 9, 10 and 12 days post onset (d.p.o), respectively. The antibody levels increased rapidly beginning at 6 d.p.o. and were accompanied by a decline in viral load. For patients in the early stage of illness (0–7 d.p.o), Ab showed the highest sensitivity (64.1%) compared to IgM and IgG (33.3% for both, p<0.001). The sensitivities of Ab, IgM and IgG increased to 100%, 96.7% and 93.3% 2 weeks later, respectively. When the same antibody type was detected, no significant difference was observed between enzyme-linked immunosorbent assays and other forms of immunoassays. Conclusions A typical acute antibody response is induced during SARS-CoV-2 infection. Serology testing provides an important complement to RNA testing in the later stages of illness for pathogenic specific diagnosis and helpful information to evaluate the adapted immunity status of patients.
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The pandemic of coronavirus disease 2019 (COVID-19) continues to affect much of the world. Knowledge of diagnostic tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is still evolving, and a clear understanding of the nature of the tests and interpretation of their findings is important. This Viewpoint describes how to interpret 2 types of diagnostic tests commonly in use for SARS-CoV-2 infections—reverse transcriptase–polymerase chain reaction (RT-PCR) and IgM and IgG enzyme-linked immunosorbent assay (ELISA)—and how the results may vary over time
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We report acute antibody responses to SARS-CoV-2 in 285 patients with COVID-19. Within 19 days after symptom onset, 100% of patients tested positive for antiviral immunoglobulin-G (IgG). Seroconversion for IgG and IgM occurred simultaneously or sequentially. Both IgG and IgM titers plateaued within 6 days after seroconversion. Serological testing may be helpful for the diagnosis of suspected patients with negative RT–PCR results and for the identification of asymptomatic infections. A cross-sectional study of hospitalized patients with COVID-19 and a longitudinal follow-up study of patients with COVID-19 suggest that SARS-CoV2-specific IgG or IgM seroconversion occurs within 20 days post symptom onset.
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Background Elucidation of the chain of disease transmission and identification of the source of coronavirus disease 2019 (COVID-19) infections are crucial for effective disease containment. We describe an epidemiological investigation that, with use of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serological assays, established links between three clusters of COVID-19. Methods In Singapore, active case-finding and contact tracing were undertaken for all COVID-19 cases. Diagnosis for acute disease was confirmed with RT-PCR testing. When epidemiological information suggested that people might have been nodes of disease transmission but had recovered from illness, SARS-CoV-2 IgG serology testing was used to establish past infection. Findings Three clusters of COVID-19, comprising 28 locally transmitted cases, were identified in Singapore; these clusters were from two churches (Church A and Church B) and a family gathering. The clusters in Church A and Church B were linked by an individual from Church A (A2), who transmitted SARS-CoV-2 infection to the primary case from Church B (F1) at a family gathering they both attended on Jan 25, 2020. All cases were confirmed by RT-PCR testing because they had active disease, except for A2, who at the time of testing had recovered from their illness and tested negative. This individual was eventually diagnosed with past infection by serological testing. ELISA assays showed an optical density of more than 1·4 for SARS-CoV-2 nucleoprotein and receptor binding domain antigens in titres up to 1/400, and viral neutralisation was noted in titres up to 1/320. Interpretation Development and application of a serological assay has helped to establish connections between COVID-19 clusters in Singapore. Serological testing can have a crucial role in identifying convalescent cases or people with milder disease who might have been missed by other surveillance methods. Funding National Research Foundation (Singapore), National Natural Science Foundation (China), and National Medical Research Council (Singapore).
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Objective To evaluate viral loads at different stages of disease progression in patients infected with the 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the first four months of the epidemic in Zhejiang province, China. Design Retrospective cohort study. Setting A designated hospital for patients with covid-19 in Zhejiang province, China. Participants 96 consecutively admitted patients with laboratory confirmed SARS-CoV-2 infection: 22 with mild disease and 74 with severe disease. Data were collected from 19 January 2020 to 20 March 2020. Main outcome measures Ribonucleic acid (RNA) viral load measured in respiratory, stool, serum, and urine samples. Cycle threshold values, a measure of nucleic acid concentration, were plotted onto the standard curve constructed on the basis of the standard product. Epidemiological, clinical, and laboratory characteristics and treatment and outcomes data were obtained through data collection forms from electronic medical records, and the relation between clinical data and disease severity was analysed. Results 3497 respiratory, stool, serum, and urine samples were collected from patients after admission and evaluated for SARS-CoV-2 RNA viral load. Infection was confirmed in all patients by testing sputum and saliva samples. RNA was detected in the stool of 55 (59%) patients and in the serum of 39 (41%) patients. The urine sample from one patient was positive for SARS-CoV-2. The median duration of virus in stool (22 days, interquartile range 17-31 days) was significantly longer than in respiratory (18 days, 13-29 days; P=0.02) and serum samples (16 days, 11-21 days; P<0.001). The median duration of virus in the respiratory samples of patients with severe disease (21 days, 14-30 days) was significantly longer than in patients with mild disease (14 days, 10-21 days; P=0.04). In the mild group, the viral loads peaked in respiratory samples in the second week from disease onset, whereas viral load continued to be high during the third week in the severe group. Virus duration was longer in patients older than 60 years and in male patients. Conclusion The duration of SARS-CoV-2 is significantly longer in stool samples than in respiratory and serum samples, highlighting the need to strengthen the management of stool samples in the prevention and control of the epidemic, and the virus persists longer with higher load and peaks later in the respiratory tissue of patients with severe disease.
We profiled the serological responses to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) nucleocapsid (N) protein and spike (S) glycoprotein. The majority of the patients developed robust antibody responses between 17 and 23 days after illness onset. Delayed, but stronger antibody responses were observed in critical patients. © The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: [email protected]
Africa is boosting its capacity to respond to COVID-19, but lack of solidarity will cost lives, warns Africa CDC head John Nkengasong. Africa is boosting its capacity to respond to COVID-19, but lack of solidarity will cost lives, warns Africa CDC head John Nkengasong. “African countries have funds to pay for reagents but cannot buy them.”