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Determination of the UV Inactivation Constant under 280 nm UV LED Irradiation for SARS‐CoV‐2


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The ongoing emergency provoked by the SARS‐CoV‐2 pandemic demands the development of technologies to mitigate the spread of infection, and UV irradiation is a technique that can efficiently address this issue. However, proper use of UV equipment for disinfection requires an understanding of how the effects on SARS‐CoV‐2 are dependent on certain parameters. In this work, we determined the UV‐C inactivation constant k for SARS‐CoV‐2 using an LED source at λ=280 nm. Specifically, a Log3 reduction was measured after irradiation for 24 minutes with a delivered UV‐C dose of 23 J/m2. By multitarget model fitting, n=2 and k=0.32±0.02 m2/J were obtained. A lag time for the inactivation effect was also observed, which was attributed to the low irradiation levels used to perform the study. The combination of k and delay time allows for reliable estimation of disinfection times in small, closed environments.
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Photochemistry and Photobiology, 20**, **: **
Research Article
Determination of the UV Inactivation Constant Under 280 Nm UV LED
Irradiation for SARS-CoV-2
, Signorini Lucia
, Cattaneo Luciano
, Della Corna Lorenzo
, Guercilena Andrea
DAlessandro Sarah
, Ferrante Pasquale
and Delbue Serena
Light and Colour Engineering s.r.l, Piazza Della Repubblica, Mediglia, Italy
Laboratory of Molecular Virology, Department of Biomedical, Surgical and Dental Sciences, University of Milan, Milan, Italy
Mireide Electronics s.r.l., Lodi, Italy
Simaco Elettromeccanica s.r.l., Lodi, Italy
Received 8 September 2021, accepted 14 May 2022, DOI: 10.1111/php.13653
The ongoing emergency provoked by the SARS-CoV-2 pan-
demic demands the development of technologies to mitigate
the spread of infection, and UV irradiation is a technique
that can efciently address this issue. However, proper use of
UV equipment for disinfection requires an understanding of
how the effects on SARS-CoV-2 are dependent on certain
parameters. In this work, we determined the UV-C inactiva-
tion constant k for SARS-CoV-2 using an LED source at
λ=280 nm. Specically, a Log3 reduction was measured
after irradiation for 24 min with a delivered UV-C dose of
23 J m
. By multitarget model tting, n=2 and
k=0.32 0.02 m
were obtained. A lag time for the
inactivation effect was also observed, which was attributed to
the low irradiation levels used to perform the study. The
combination of k and delay time allows for reliable estima-
tion of disinfection times in small, closed environments.
BSL-3 biosafety level-3;
CPEs cytopathic effects;
DMEM dulbeccos modied eagles medium;
DNA deoxyribonucleic acid;
DPBS dulbeccos phosphate-buffered saline;
FBS fetal bovine serum;
LED light emitting diode;
min minutes;
MOI multiplicity of infection;
NSP nasal pharyngeal swab;
PFU plaque forming unit;
qRTPCR quantitative reverse transcriptase-PCR;
RNA ribonucleic acid;
severe acute respiratory syndrome-coronavirus-2;
t time;
UV Ultraviolet;
The recent emergency originating in 2020 by the spread of Sev-
ere Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)
infection has increased attention on disinfection methods to pre-
vent infections and reduce the spread of the virus.
In particular, Ultra Violet (UV) light irradiation has received
increasing attention since it is a well-established, simple, effec-
tive, noncontact method to inactivate pathogenic microorganisms,
such as viruses, bacteria and spores (1). UV irradiation can be
efciently used to inactivate viruses in saliva droplet suspensions
oating in closed environments or deposited over surfaces or
equipment (2).
The UV light spectrum covers the range of 100400 nm and
is divided into UV-A (400315 nm), UV-B (315280 nm) and
UV-C (100280 nm) regions. Light from the UV-C and UV-B
regions can be absorbed by DNA, RNA and proteins of microor-
ganisms, causing alterations in their molecular structures and
thereby affecting their replication process. The efciency of UV
exposure depends on the wavelength, with a maximum efciency
at approximately 260265 nm. The structure of microorganisms
also plays a role, so the actual efciency may vary between spe-
cies (1).
Microorganisms irradiated with UV light are exposed to a
dose D=I*t(J m
), which is a function of irradiance I
(W m
) and exposure time t(s). The fraction of survival, i.e.
the fraction of microorganisms still active after irradiation time t,
can be described as F=exp(k*D), where kis the UV rate con-
stant (m
) and is species- and wavelength-dependent. krepre-
sents the susceptibility of a particular pathogen to UV exposure:
high values of kare associated with fast decay and thus fast dis-
infection, while low values of k are associated with slow decay
and longer disinfection times (2).
A review of the effects of UV-C light on coronaviruses was
reported by Kowalski et al.(3). Recently, many works have
focused specically on SARS-CoV-2, reporting that signicant
inactivation can be successfully achieved using UV-C light (4
10). In particular, Minamikawa et al. used three Light Emitting
*Corresponding author email: (Silvia Bif)
These authors equally contributed to the project.
©2022 The Authors. Photochemistry and Photobiology published by Wiley Peri-
odicals LLC on behalf of American Society for Photobiology.
This is an open access article under the terms of the Creative Commons Attribution
License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
Diode (LED) light sources exhibiting peaks at λ=265, λ=280
and λ=300 nm and found that Log3 inactivation was achieved
when the virus was exposed to doses of 18, 30 and 230 J m
respectively; the effects of wavelength on SARS-CoV-2 inactiva-
tion were also measured (9). LEDs with a peak at 280 nm are a
solid technology commercially available at low cost and with
stable emission over time. For these reasons, λ=280 5nm
LEDs are ideal for developing new low-cost devices. In this
work, we focused on the interaction between SARS-CoV-2 under
wet conditions using viral particles suspended in liquid media
and UV-C light irradiation at λ=280 5 nm by measuring in
detail the inactivation of SARS-CoV-2 over time and determin-
ing its UV-C inactivation constant k. By using extremely low
irradiation values, which resemble working conditions for UV-C
disinfection in small, closed environments, we studied for the
rst time the early stages of SARS-CoV-2 inactivation and
observed a lag time in the response of the inactivation process.
UV illumination system. The light source used in this study was a
modied version of a commercial lamp (KATARI
) built and marketed
by Simaco Elettromeccanica, Italy. Simaco supplied a lamp that was
modied with respect to those that the company builds and markets. The
lamp was depowered to allow low irradiance levels in small laboratory
environments, such as hoods. Simaco also supplied a screening device to
contain UV-C light and a commercial power meter (Spectroradiometer
JEDI Technische Instrumente specbos 1211 UV-2-LAN) to measure
irradiance on site. The lamp was equipped with three UV-C LEDs
emitting in the range of λ=280 5 nm (Figure S1) and with aluminum
reectors that modied the beam in a controlled way, enabling increased
radiation emission levels and improved uniformity on the target. The
distance between the light source and the samples must be almost 10
times the linear dimension of the source module (or the sensor) to avoid
reading errors due to the cosine law followed by sensor devices (11).
Given the geometrical characteristics of the lamp, the samples were
placed at a distance of 0.57 m from the lamp. Calculations were
performed for incident irradiance, with distance measured from the uid
surface. Irradiance on the samples was measured to be I=0.182 W m
At such low irradiation values, it was possible to control the UV-C doses
delivered to the samples through exposure time with negligible
experimental error. Exposure times were chosen in the range of 0
30 min. In three independent experiments, irradiation was performed for
t=3, 6, 12 and 24 min, while a single experiment was performed with
irradiation for t=3, 7.5, 15 and 30 min.
Isolation of SARS-CoV-2 from nasopharyngeal swab. Nasal
pharyngeal swab (NPS) was collected upon approval of the Local Ethical
Committee and signature of the informed consent (Fondazione Ca0
Granda, Ospedale Maggiore, Milano, Italy approved the protocol
456_2020, on May 2020). SARS-CoV-2 was isolated from 500 μLof
NSP of a COVID-19 patient, added to Vero cells (ATCC CCL-81), and
maintained in complete medium composed of Dulbeccos modied
Eagles medium (DMEM) high glucose containing 10% heat-inactivated
fetal bovine serum (FBS), 2 mM L-glutamine and antibiotics (Euroclone,
Italy) at 80% conuence; the inoculum was removed after a 3-h
incubation at 37°C with 5% CO
, and the cells were incubated at 37°C
and 5% CO
for 72 h, when cytopathic effects (CPEs) were evident.
Isolation of the virus was conrmed by specic quantitative reverse
transcriptase-PCR (qRTPCR) (12), which targets the N1 region of the
SARS-CoV-2 nucleocapsid gene, and by complete genome sequencing,
as previously described (13). The isolated strain was subsequently titrated
by plaque assay using dilution factors ranging from 10
to 10
and was
used at a multiplicity of infection (MOI) of 0.01 in subsequent
experiments. The complete nucleotide sequence of the isolated SARS-
CoV-2 strain was deposited at GenBank at NCBI (accession number:
SARS-CoV-2 irradiation. Before irradiation, the viral stock was
diluted in DMEM high glucose with sodium pyruvate, without L-
glutamine, 2 mML-glutamine, and 1X penicillin and streptomycin. Then,
60 μL of this solution (10 000 Plaque Forming Unit -PFU- mL
) was
added in triplicate to a 24-well plate. Medium without virus (mock) was
used as a control. The light source was placed over the plate at a height
of 0.57 m. Irradiation was performed for 3, 6, 7.5, 12, 15, 24 and 30 min
(N). A copy plate with complete medium containing the virus was
subjected to the same irradiation steps with a regular light lamp (zero-
irradiation control, N
). The experiment was repeated three times.
Evaluation of antiviral activity. The day before irradiation, Vero E6
(ATCC CRL-1586) cells were seeded into 96-well plates at a density of
1.3 ×10
cells per well in complete medium and incubated at 37°C with
5% CO
. Immediately after irradiation following the SARS-CoV-2
irradiation scheme (3, 6, 7.5, 12, 15, 24 and 30 min of irradiation [N],
zero-irradiation control [N
] and mock), 30 μL of each viral suspension
(MOI equivalent to 0.01) was added to Vero E6 cells, which were
inoculated for 2 h at 37°C with 5% CO
. The viral inoculum was
removed, the cells were washed with Dulbeccos phosphate-buffered
saline (DPBS), 200 μL of complete medium was added, and the plate
was incubated at 37°C with 5% CO
. On day 2 postinfection, CPEs were
evaluated under a light microscope. Culture medium was harvested, and
RNA was isolated using the NucleoSpin RNA Virus kit (Macherey
Nagel, Germany) following the manufacturersprotocol. Quantication of
viral copy numbers was evaluated via qRTPCR (12). Data are expressed
as the fraction of residual activity, F=N/N
, where N
and Nrepresent
the viral amount (SARS-CoV-2 copies mL
) in the wells not subjected
and subjected to irradiation, respectively.
Evaluation of the virucidal activity by plaque assay. The virucidal
effect of UV-C irradiation was evaluated by means of a plaque assay
performed on the infected cell medium harvested from the antiviral
activity experiments. For each time point, performed in triplicate,
supernatants obtained from the infected and irradiated cells were pooled
into one data point. Moreover, 400 μL of each well of Vero E6 cells was
added in duplicate and plated the day before in a 6-well plate in
complete medium (7.5 ×10
cells per well). Briey, after 2 h of
inoculation with the pooled viral suspensions, the inocula were removed,
and the cells were covered with a 0.3% agarose gel, dissolved in
complete medium, and incubated for 48 h at 37°C with 5% CO
. Cells
were then xed with 4% formaldehyde solution and, after agarose
removal, stained with 0.5% methylene blue. Plaques were counted, and
the results are expressed as the fraction of residual activity, F=N/N
where N
and Nrepresent the plaque number (PFU mL
) obtained in
the wells containing the medium of cells infected with zero irradiation
and the irradiated samples, respectively.
All experiments were performed in a BioSafety Level-3 (BSL-3) labo-
Cytopathic effects were clearly observed in SARS-CoV-2-
infected Vero E6 cells not subjected to irradiation (zero-
irradiation control), while the CPEs progressively decreased in
infected cells subjected to an increased dose of radiation,
whereby cell morphology was largely comparable to that of
mock cells after 24 min of irradiation (data not shown).
Viral activity after UV-C exposure was measured by qRT
PCR and plaque assay techniques. The calculations for UV dose
were made using the incident irradiance value and were not cor-
rected for either absorbance or sample depth. The absorbance of
the DMEM at 280 nm was measured and it was 5.3 cm
ure S2), while the sample depth was calculated to be 300 μm.
The actual transmittance through the 300 μm was estimated to
be 0.69 (69%). The data shown in Fig. 1are expressed as a frac-
tion of residual activity, F=N/N
, where N
and Nrepresent the
viral amount before and after irradiation, respectively. As
expected, the fraction of survival was signicantly affected by
UV-C irradiation. The linear scale stresses the difference in sig-
nicance of the two measurement techniques. qRT-PCR (blue
stars) measures the total amount of viral RNA recovered without
distinguishing between infectious viruses and nucleic acids
derived from inactivated viruses and thus provides a higher
2 BifSilvia et al.
count, especially at low doses, i.e. low exposure times. In con-
trast, the plaque assay (red dots) quanties the actual viral resid-
ual activity and is thus a more suitable indicator of the amount
of infectious virus. Figure 2shows the data obtained from the
plaque assay on a semilogarithmic scale, and it can be appreci-
ated that the viral activity decreases up to 10
in the time range
explored. A Log
reduction was measured after an irradiation
time of 24 min and a delivered UV-C dose of 23 J m
. Repre-
sentative data (irradiation for 0, 3, 24 and 30 min) from three
independent plaque assays are shown in Fig. 3.
It is evident from Fig. 2that the data can be approximated
with a single exponential, but the value of the intercept at D=0
is greater than one. Additional data should be collected to better
dene the early stages of inactivation, but in this case, the decay
may be better approximated by a shoulder curve, starting out
horizontally and developing a full exponential decay only after a
few minutes of irradiation. Shoulder curves can be described by
the multitarget model, which assumes that to inactivate a single
microorganism, a critical number nof discrete sites has to be hit.
The fraction of residual activity is then expressed as
F¼11exp kDðÞ½
where nis the multitarget exponent and is unique for each
species (1,2,14). According to the multitarget model, the nvalue
can be found by extrapolating the exponential stage data to the
y-intercept (2). Data were rst tted to a single exponential curve
to extrapolate the intercept with the y-axis. The value of the
intercept was y=2.0. The whole set of data was then tted to
Eq. (1), where n=2.0 was imposed and the only free parameter
left was k. As a result, the kvalue obtained was
k=0.32 0.02 m
. In both cases, the LevenbergMar-
quardt tting algorithm was used.
The literature on UV-C inactivation of SARS-CoV-2 has mainly
focused on working conditions characterized by relatively high
irradiance and short distances between the light source and virus
sample. This work has been extremely important to conrm the
efcacy of UV-C irradiation on SARS-CoV-2 and to establish
the working conditions for its rapid and effective inactivation.
The studies of Storm (7) and Biasin (8) were conducted using
low-pressure mercury lamps (254 nm) and irradiating the virus
sample with 10.82 and 8.49 W m
respectively; in the work of
Minamikawa (9), deep ultraviolet light-emitting diodes (265, 280
and 300 nm) were used, with effective irradiance values of 0.92,
0.83 and 9.25 W m
respectively. In these works, the SARS-
CoV-2 inactivation curves observed are well described by single
exponential decays or, as in the work of Storm (7) under dry
conditions, by a double exponential. The particularly low irradi-
ance level used in the present study I=0.182 W m
, was cho-
sen instead to mimic irradiation conditions that could be typical
in UV-C disinfection of small, closed environments, e.g. with
UV-C lamps set on the walls and ceilings of small environments.
As a reference, with a lamp emitting 0.1 W in Lambertian mode
placed 3.3 m high on the ceiling of an ofce, the irradiance on a
desk (0.7 m high) would be on the order of 4.7 ×10
on the surface perpendicular to the optical axes.
We found that when SARS-CoV-2 is treated with low-
intensity UV-C light, the shape of its inactivation curve differs
from that observed using high-intensity irradiation. This behavior
was unexpected and it needs to be explored. Previous works
forced single-stage decay through zero exposure concentration.
We did not make such an assumption in our study, which led to
the observation that there may be a shoulder associated with the
inactivation of the virus. Future studies should include additional
data collection in the region below the lowest UV-C dose
explored in this work to better describe the early-stage behavior
of virus inactivation. The shoulder curve reported in this work is
in contrast to the recent observation that inactivation of SARS-
CoV-2 under wet conditions is better described by a single decay
(7). Such a difference in behavior can be attributed precisely to
the different irradiation levels used in the two works. Given the
low irradiation level used, the lag in response observed in this
work can be explained by the presence of a threshold dose that
has to be reached to provoke signicant damage (1). Once the
threshold dose has been reached, the inactivation process begins/
progresses, and the single exponential decay is restored. Indeed,
Figure 1. UV-C-irradiated SARS-CoV-2 (MOI 0.01) residual activity in
Vero E6 cells in vitro. SARS-CoV-2 was irradiated for 330 min and
then inoculated into Vero E6 cells, which were harvested 48 h postinfec-
tion. The residual activity of the virus was assessed by qRTPCR (red
dot) and plaque assay (blue stars). All experiments were conducted in
Figure 2. Data from the SARS-CoV-2 plaque assay on a semilogarith-
mic scale. Data are tted with a single exponential model F=exp
(k*D) (dashed line) and with a multitarget model F=1[1exp
(solid line).
Photochemistry and Photobiology 3
the value of the UV-C inactivation constant determined here,
k=0.32 0.02 m
, is consistent with that reported in the
work of Minamikawa (9), where a kvalue of 0.30 m
λ=280 nm was found.
The shoulder effect has also been observed in other studies on
coronaviruses (15) and might be particularly important for the
safe application of UV-C disinfection in daily situations, which
requires further investigation. The presence of this effect suggests
that irradiation times for disinfection cannot be estimated solely
based on extrapolation from measurements conducted at short dis-
tances but should consider the irradiation value actually delivered
on a given surface, which diminishes as the square of the distance
from the light source. According to Kowalski et al.(2), the ampli-
tude of the shoulder, i.e. the delay in inactivation, is inversely
proportional to the irradiation ux; thus, the delay would be
increased on surfaces far from the UV-C source.
Overall, we conrmed that UV-C LED disinfection could be
useful to increase the containment of SARS-CoV-2 spread, espe-
cially in medical environments and community settings, where
devices equipped with UV-C LEDs might be employed. It
should also be noted that limited, accidental exposure to UV-C
LED light (e.g. accidentally stepping into a room where UV-C
LEDs are on) most likely will not exceed the safety exposure
level, which is dened as 30 J m
by the guidelines of
ICNIRP and IRPA/INIRC (16,17).
The main limitation of this paper was the lack of a description
of the kvalue and a quantitative description of the inactivation
delay time under dry conditions versus wet conditions. Future
studies in this direction would allow us to dene a reliable esti-
mate of disinfection times on different types of surfaces and
environments. Moreover, it is necessary to better dene the pos-
sibility of using UV-C LED irradiation to inactivate SARS-CoV-
2 in body uids, such as saliva and/or respiratory samples that
may be easily found on surfaces, and in aerosols composed of
different sizes of microdroplets.
AcknowledgementsThe study was supported by Simaco
Elettromeccanica s.r.l. Simaco also supplied a lamp that was modied
with respect to those that Simaco builds and markets. The lamp was
depowered to allow low irradiance levels in small laboratory
environments, such as hoods. Simaco supplied a screening device to
contain UV-C light and a commercial power meter to measure irradiance
on site. The authors would like to thank Prof. Buscaglia and his team for
the scientic discussion. Open Access Funding provided by Universita
degli Studi di Milano within the CRUI-CARE Agreement.
The authors declare no conicts of interest. SIMACO Elet-
tromeccanica s.r.l. did not inuence the work or the results
reported in this paper.
Figure 3. Plaque assays. Representative data from three independent assays after (a) no irradiation (0 min) and (b) 3 min, (c) 24 min and (d) 30 min of
4 BifSilvia et al.
L.C., L.D. and S.D. designed the study. L.S. and S.DA. per-
formed the measurements. S.B., L.C., S.D. and P.F. analyzed the
data. S.B., L.C. and S.D. wrote the paper.
Additional supporting information may be found online in the
Supporting Information section at the end of the article:
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Photochemistry and Photobiology 5
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Full-text available
Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmissions during the on-going COVID-19 global pandemic and in the future. Ultraviolet (UV) devices emitting UVC irradiation (200-280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level (BSL) 3 laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths (222 nm to 282 nm) from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL-2) during UV disinfection tests. This study provides fundamental information for UVC action on SARS-CoV-2 and guidance for achieving reliable disinfection performance of UVC devices. IMPORTANCE UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, transportation and healthcare settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the on-going COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222nm provided the best disinfection performance. Interestingly, 222 nm irradiation has been found to be safe for human exposure up to thresholds that are beyond effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface transmissions.
Full-text available
The potential virucidal effects of UV-C irradiation on SARS-CoV-2 were experimentally evaluated for different illumination doses and virus concentrations (1000, 5, 0.05 MOI). At a virus density comparable to that observed in SARS-CoV-2 infection, an UV-C dose of just 3.7 mJ/cm2 was sufficient to achieve a more than 3-log inactivation without any sign of viral replication. Moreover, a complete inactivation at all viral concentrations was observed with 16.9 mJ/cm2. These results could explain the epidemiological trends of COVID-19 and are important for the development of novel sterilizing methods to contain SARS-CoV-2 infection.
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Inactivation technology for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is certainly a critical measure to mitigate the spread of coronavirus disease 2019 (COVID-19). A deep ultraviolet light-emitting diode (DUV-LED) would be a promising candidate to inactivate SARS-CoV-2, based on the well-known antiviral effects of DUV on microorganisms and viruses. However, due to variations in the inactivation effects across different viruses, quantitative evaluations of the inactivation profile of SARS-CoV-2 by DUV-LED irradiation need to be performed. In the present study, we quantify the irradiation dose of DUV-LED necessary to inactivate SARS-CoV-2. For this purpose, we determined the culture media suitable for the irradiation of SARS-CoV-2 and optimized the irradiation apparatus using commercially available DUV-LEDs that operate at a center wavelength of 265, 280, or 300 nm. Under these conditions, we successfully analyzed the relationship between SARS-CoV-2 infectivity and the irradiation dose of the DUV-LEDs at each wavelength without irrelevant biological effects. In conclusion, total doses of 1.8 mJ/cm² for 265 nm, 3.0 mJ/cm² for 280 nm, and 23 mJ/cm² for 300 nm are required to inactivate 99.9% of SARS-CoV-2. Our results provide quantitative antiviral effects of DUV irradiation on SARS-CoV-2, serving as basic knowledge of inactivation technologies against SARS-CoV-2.
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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was isolated from the oro/pharyngeal swabs of two Italian COVID-19 patients, physicians in a COVID-19 division hospital, with different courses of the disease. The complete genome sequences show that the two isolates belong to the B1.1 lineage, but contain a nucleotide mutation in the ORF6, leading to a stop codon and to the deletion of 6 amino acids in the C terminus. This deletion was unique, compared to the currently available sequences deposited in the GISAID and GenBank database. It did not affect the in vitro viral replication, neither the neutralizing activities of the patients' antibodies. Based on homology analysis with other Coronaviruses, the two isolated lacked the ORF6 aminoacidic portion responsible for the inhibition of the antiviral Interferon (IFN)-based host response. IFN seems to have a dual role of in SARS-CoV-2 infected patients: not only antiviral activity, but also a detrimental role in case of excessive production. A deletion in the SARS-CoV-2 ORF6 protein might have a specific, still unknown role in the viral pathogenesis.
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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has devastated global public health systems and economies, with over 52 million people infected, millions of jobs and businesses lost, and more than 1 million deaths recorded to date. Contact with surfaces contaminated with droplets generated by infected persons through exhaling, talking, coughing and sneezing is a major driver of SARS-CoV-2 transmission, with the virus being able to survive on surfaces for extended periods of time. To interrupt these chains of transmission, there is an urgent need for devices that can be deployed to inactivate the virus on both recently and existing contaminated surfaces. Here, we describe the inactivation of SARS-CoV-2 in both wet and dry format using radiation generated by a commercially available Signify ultraviolet (UV)-C light source at 254 nm. We show that for contaminated surfaces, only seconds of exposure is required for complete inactivation, allowing for easy implementation in decontamination workflows.
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The coronavirus SARS-CoV-2 pandemic became a global health burden. We determined the susceptibility of SARS-CoV-2 to irradiation with ultraviolet light. The virus was highly susceptible to ultraviolet light. A viral stock with a high infectious titer of 5 × 10⁶ TCID50/ml was completely inactivated by UVC irradiation after nine minutes of exposure. The UVC dose required for complete inactivation was 1048 mJ/cm². UVA exposure demonstrated only a weak effect on virus inactivation over 15 minutes. Hence, inactivation of SARS-CoV-2 by UVC irradiation constitutes a reliable method for disinfection purposes in health care facilities and for preparing SARS-CoV-2 material for research purpose.
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The spread of novel coronavirus disease 2019 (COVID-19) infections worldwide has raised concerns about the prevention and control of SARS-CoV-2. Devices that rapidly inactivate viruses can reduce the chance of infection through aerosols and contact transmission. This in vitro study demonstrated that irradiation with a deep ultraviolet light-emitting diode (DUV-LED) of 280 ±5 nm wavelength rapidly inactivates SARS-CoV-2 obtained from a COVID-19 patient. Development of devices equipped with DUV-LED is expected to prevent virus invasion through the air and after touching contaminated objects.
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A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207–222 nm) efficiently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efficiently kills airborne influenza virus and we extend those studies to explore far-UVC efficacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efficiency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm2/hour) would result in ~90% viral inactivation in ~8 minutes, 95% in ~11 minutes, 99% in ~16 minutes and 99.9% inactivation in ~25 minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations.
Technical Report
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This report addresses a topic of high current interest - the ultraviolet susceptibility of SARS-CoV-2, the virus that causes COVID-19 disease. The results of a literature review are presented and summarized to provide a basis for estimating the ultraviolet susceptibility of SARS-CoV-2, and relevant supplemental information is provided on COVID-19 based on the latest published reports. A discussion on the feasibility of using the new technology of Focused Multivector Ultraviolet light as a disinfection strategy is included.
UV light-emitting diodes (UV LEDs) are an emerging technology and a UV source for pathogen inactivation, however low UV-LED wavelengths are costly and have low fluence rate. Our results suggest that the sensitivity of human Coronavirus (HCoV-OC43 used as SARS-CoV-2 surrogate) was wavelength dependent with 267 nm ~ 279 nm > 286 nm > 297 nm. Other viruses showed similar results, suggesting UV LED with peak emission at ~286 nm could serve as an effective tool in the fight against human Coronaviruses.