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Objectives
Due to the spread of the Omicron variant, many countries have experienced COVID-19 case numbers unseen since the start of the pandemic. We aimed to compare the epidemiological characteristics of Omicron with prior variants and different strains of influenza, to provide context for public health responses.
Methods
We developed transmissi...
Context in source publication
Context 1
... additionally determined the protection rate of booster doses against infection by Omicron in the United States and Canada, as shown in Fig. 4 and reduced the number of deaths by and in those countries. These results imply that with 70% protection against Omicron (see Table 1), booster doses of currently available vaccines can significantly reduce ...
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The COVID-19 pandemic provides an opportunity to explore the impact of government mandates on movement restrictions and non-pharmaceutical interventions on a novel infection, and we investigate these strategies in early-stage outbreak dynamics. The rate of disease spread in South Africa varied over time as individuals changed behavior in response t...
Citations
... 35,36 The Omicron variant is associated with higher infectivity, antigenic changes that mediate antibody escape from an existing pre-immune population, and was found to have a transmission rate 3.4 times higher than that of the Delta variant, and 2.1 times higher than other variants in the United States. 37 Interestingly, the Omicron sub lineages are able to evade immunity in both convalescent and fully vaccinated individuals. 36,38 Convalescent sera from individuals infected with BA.1 showed significant reduction in neutralizing antibodies against the BA.4 and BA.5 strains. ...
The severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) Omicron variant of concern has been the dominant cause of worldwide COVID-19 cases since 2022. All the Omicron sublineage viruses have demonstrated high transmissibility and an ability to escape vaccine-induced immunity. While first-generation vaccines, including monovalent vaccines, continue to provide protection against severe disease, hospitalization and mortality, their efficacy against Omicron sub variants remains sparse. These vaccines have also been associated with rapidly waning protection against primary COVID-19 and COVID-19 reinfections conferred by evolving Omicron sublin-eages.. This led to the development and deployment of updated vaccines and the introduction of the bivalent booster. Through this review, we highlight the brief journey of the variants of concern leading to the dominance of Omicron and the effectiveness of the key vaccines against these variants , including the updated (bivalent) boosters.
... In addition, during the early phase of the COVID-19 pandemic, metapopulation models have been extensively used to simulate the epidemics across different areas (Chinazzi et al. 2020;Wu et al. 2020). During the late phase of the COVID-19 pandemic, metapopulation models have been applied with sufficient data to explore infectivity and fatality of SARS-CoV-2 mutations (Xue et al. 2022). ...
In this paper, we propose a two-patch SIRS model with a nonlinear incidence rate: [Formula: see text] and nonconstant dispersal rates, where the dispersal rates of susceptible and recovered individuals depend on the relative disease prevalence in two patches. In an isolated environment, the model admits Bogdanov-Takens bifurcation of codimension 3 (cusp case) and Hopf bifurcation of codimension up to 2 as the parameters vary, and exhibits rich dynamics such as multiple coexistent steady states and periodic orbits, homoclinic orbits and multitype bistability. The long-term dynamics can be classified in terms of the infection rates [Formula: see text] (due to single contact) and [Formula: see text] (due to double exposures). In a connected environment, we establish a threshold [Formula: see text] between disease extinction and uniform persistence under certain conditions. We numerically explore the effect of population dispersal on disease spread when [Formula: see text] and patch 1 has a lower infection rate, our results indicate: (i) [Formula: see text] can be nonmonotonic in dispersal rates and [Formula: see text] ([Formula: see text] is the basic reproduction number of patch i) may fail; (ii) the constant dispersal of susceptible individuals (or infective individuals) between two patches (or from patch 2 to patch 1) will increase (or reduce) the overall disease prevalence; (iii) the relative prevalence-based dispersal may reduce the overall disease prevalence. When [Formula: see text] and the disease outbreaks periodically in each isolated patch, we find that: (a) small unidirectional and constant dispersal can lead to complex periodic patterns like relaxation oscillations or mixed-mode oscillations, whereas large ones can make the disease go extinct in one patch and persist in the form of a positive steady state or a periodic solution in the other patch; (b) relative prevalence-based and unidirectional dispersal can make periodic outbreak earlier.
... It is reported that the Omicron variant has traits of faster transmission and immune escape but reduced lethality compared with previously identified variants of SARS-CoV-2 [20,21], which has led to more insidious community transmission and greater pressure for prevention and control. Currently, booster vaccination against COVID-19 has been fully promoted worldwide in response to the Omicron epidemic. ...
This study aims to explore the relationship between the doses of inactivated COVID-19 vaccines received and SARS-CoV-2 Omicron infection in the real-world setting, so as to preliminarily evaluate the protective effect induced by COVID-19 vaccination. We conducted a test-negative case-control study and recruited the test-positive cases and test-negative controls in the outbreak caused by Omicron BA.2 in April 2022 in Guangzhou, China. All the participants were 3 years and older. The vaccination status between the case group and the control group was compared in the vaccinated and all participants, respectively, to estimate the immune protection of inactivated COVID-19 vaccines. After adjusting for sex and age, compared with a mere single dose, full vaccination of inactivated COVID-19 vaccines (OR = 0.191, 95% CI: 0.050 to 0.727) and booster vaccination (OR = 0.091, 95% CI: 0.011 to 0.727) had a more superior protective effect. Compared with one dose, the second dose was more effective in males (OR = 0.090), as well as two doses (OR = 0.089) and three doses (OR = 0.090) among individuals aged 18–59. Whereas, when compared with the unvaccinated, one dose (OR = 7.715, 95% CI: 1.904 to 31.254) and three doses (OR = 2.055, 95% CI: 1.162 to 3.635) could contribute to the increased risk of Omicron infection after adjusting for sex and age. Meanwhile, by contrast with unvaccinated individuals, the result of increased risk was also manifested in the first dose in males (OR = 12.400) and one dose (OR = 21.500), two doses (OR = 1.890), and a booster dose (OR = 1.945) in people aged 18–59. In conclusion, the protective effect of full and booster vaccination with inactivated COVID-19 vaccines exceeded the incomplete vaccination, of which three doses were more effective. Nevertheless, vaccination may increase the risk of Omicron infection compared with unvaccinated people. This may result from the transmission traits of BA.2, the particularity and stronger protection awareness of the unvaccinated population, as well as the ADE effect induced by the decrease of antibody titers after a long time of vaccination. It is crucial to explore this issue in depth for the formulation of future COVID-19 vaccination strategies.
... Therefore, a decreasing trend would be expected, both because of the decreasing weight of the fragile fraction compared to the overall group and because of the harvesting effect, caused by excess mortality in the most fragile fraction. It should be added that the all-cause mortality considered is not cumulative mortality, but mortality which occurs month by month.The complementary explanatory hypotheses of this anomalous increase in mortality can only be partly traced back to the well-documented lower lethality of the Omicron variant compared with the previous variants: up to 11 times less lethal according to North American and South African data [20], or even 30 times less lethal according to the Italian data of the Abruzzo Region [21]. ...
The COVID-19 pandemics has had an unprecedented global impact, and the COVID-19 mass vaccination campaign has been commonly regarded as crucial to overcome the pandemics. Since all-cause mortality is the best way to measure the consequences of a health intervention, the present study was devised to analyze the all-cause mortality data of the United Kingdom (UK), which are made publicly available broken down by vaccination status. Data from January to May 2022 were retrospectively collected and analyzed according to age groups and vaccination status and the relative risk (RR) for all-cause mortality was calculated in comparison to the corresponding unvaccinated groups. All-cause mortality RR was also calculated from January to May 2021 for vaccinated people. Results show that the all-cause mortality RR was higher in people who received one or two doses of COVID-19 vaccines throughout the whole period and in any of the age groups considered. People vaccinated with three doses more than 21 days earlier had RRs lower than unvaccinated people, which however linearly increased over time. RR in vaccinated people of all ages in comparison to unvaccinated people were lower in January-May 2021, however they steadily grew over time. The finding that all-cause mortality RR in vaccinated in comparison to unvaccinated people increases over time requires careful examination to understand the underlying factors. Meanwhile, all the other major countries should undertake a systematic collection of all-causes mortality broken down by vaccination status, and mass vaccination campaigns should be suspended.
... In addition, vaccine booster programmes have been successful in partially restoring effectiveness against severe disease and death when levels of existing vaccine protection have been eroded by the emergence of new variants that have resulted in immunological escape. [2][3][4] Many countries are now considering how best to schedule regular boosting to protect against ongoing endemic circulation of the virus as well as against future epidemic waves with Omicron subtypes or new variants. The benefit of such strategies in any given population will depend on the current stage of their vaccine programme, including the supply of vaccine doses and the extent that these doses are matched to the current circulating strains, as well as the magnitude of the epidemic that has been experienced to date and thus the extent of infection-acquired immunity. ...
Background Vaccines have reduced severe disease and death from COVID-19. However, with evidence of waning efficacy coupled with continued evolution of the virus, health programmes need to evaluate the requirement for regular booster doses, considering their impact and cost-effectiveness in the face of ongoing transmission and substantial infection-induced immunity.
Methods and findings We developed a combined immunological-transmission model parameterised with data on transmissibility, severity, and vaccine effectiveness. We simulated SARS-CoV-2 transmission and vaccine rollout in characteristic global settings with different population age-structures, contact patterns, health system capacities, prior transmission, and vaccine uptake. We quantified the impact of future vaccine booster dose strategies with both original and variant-adapted vaccine products, in the presence of both continuing transmission of Omicron subvariants and considering the potential future emergence of new variants with modified transmission, immune escape, and severity properties. We found that regular boosting of the oldest age group (75+) is the most efficient strategy, although large numbers of hospitalisations and deaths can be averted by extending vaccination to younger age groups. In countries with low vaccine coverage and high infection-derived immunity, boosting older at-risk groups is more effective than continuing primary vaccination into younger ages. These findings hold if even if virus drift results in a gradual reduction in vaccine effectiveness over time due to immune escape. In a worst-case scenario where a new variant emerges that is 10% more transmissible, as severe as Delta, and exhibits substantial further immune escape, demand on health services could be similar to that experienced during 2020.
Conclusions Regular boosting of the high-risk population remains an important tool to reduce morbidity and mortality from current and future SARS-CoV-2 variants. The cost-effectiveness of boosting is difficult to assess given the ongoing uncertainty in the likelihood of future variants and their properties but focusing vaccination in the highest-risk cohorts remains the most efficient strategy to reduce morbidity and mortality.
... In contrast to its strong infectivity [4,5], a number of epidemiological studies indicated that the clinical severity of infection with the Omicron VOC was lower than with the Delta VOC [6][7][8][9][10][11][12]. However, the clinical severity in the COVID-19 cases was probably influenced not only by the nature of the viral variant but also by booster vaccine coverage [6,[13][14][15][16], medical accessibility, availability of novel oral antiviral treatments and life expectancy before the pre-COVID-19 era in the population. ...
To assess temporal changes to the risk of death in COVID-19 cases caused by the Omicron variant, we calculated age-standardized case fatality rates (CFR) in patients aged ≥40 years over nine diagnostic periods (3 January to 28 August 2022) in ten Japanese prefectures (14.8 million residents). Among 552,581 study subjects, we found that there were 1836 fatalities during the isolation period (up to 28 days from date of onset). The highest age-standardized CFR (0.85%, 95% confidence interval (CI):0.78–0.92) was observed in cases diagnosed in the second 4-week period (January 31 to February 27), after which it declined significantly up to the 6th 4-week period (0.23%, 95% CI: 0.13–0.33, May 23 to June 19). The CFR then increased again but remained at 0.39% in the eighth period (July 18 to August 28). The CFR in cases with the BA.2 or BA.5 sublineages in the age range 60–80 years was significantly lower than that with BA.1 infections (60 years: 0.19%, 0.02%, 0.053%, respectively; 70 years: 0.91%, 0.33%, 0.39%; ≥80 years: 3.78%, 1.96%, 1.81%, respectively). We conclude that the risk of death in Japanese COVID-19 patients infected with Omicron variants declined through February to mid-June 2022.
... It has been shown that during the Omicron-predominant period, the number of cases was on median higher than during the wild-type-and Deltapredominant periods. Although the spread of the different VOCs could be related to the control strategies (lockdown, surgical mask use, etc.), the increased transmissibility of Omicron is supported by several studies that estimated that the Omicron variant can infect 3 to 6 times more people than the Delta strain [30][31][32]. However, transmissibility should be considered in relation to disease severity. ...
Background:
The COVID-19 epidemic had a rapid spread worldwide with a continuous and fast mutation of the virus, resulting in the emergence of several variants of concern (VOC). The aim of this study was to evaluate the severity of each VOC among SARS-CoV-2 infected subjects by investigating deaths, ICU admissions, intubations, and severe critical symptoms.
Methods:
An ecological observational study was performed to evaluate mortality rates and clinical characteristics of 321,490 unvaccinated Sicilian SARS-CoV-2 cases observed from 2 March 2020 to 27 March 2022. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by multivariate logistic regression analysis evaluating factors determining a clinical worsening.
Results:
Delta (adj-OR 3.00, 95% Cls 2.70-3.33) and wild-type (adj-OR 2.41, 95% Cls 2.2-2.62) variants had a higher risk than the Omicron strain for developing critical COVID-19 necessitating intubation and eventually undergoing death. Moreover, males appeared to be significantly more susceptible to developing the worst clinical outcome considered, as did older subjects.
Conclusions:
The present study provides evidence of factors implicated in the worsening of SARS-CoV-2-infection-related clinical outcomes. The study highlighted the different roles of VOC, in particular Delta and wild-type, and being male and elderly in the development of a worse clinical outcome.
... During the 6th and 7th waves, when Omicron was the main variant, the disease was less severe than that due to the Delta variant. The Omicron variant is less virulent than conventional strains and may be less deadly than seasonal influenza (8). Patients in critical condition who needed specialized urgent care, such as intubation and extracorporeal membrane oxygenation, were seldom seen (5). ...
Japan has faced seven waves of the COVID-19 pandemic since 2020. Due to the less severe Omicron variant and the high rate of vaccination nationwide, the death rate has declined compared to that due to previous variants. In early 2022, current Prime Minister Fumio Kishida devised a new concept entitled "Living with COVID-19", encouraging a new lifestyle of living with SARS-CoV-2. Although treatment and prevention options have increased, the Omicron variant still causes deaths among the most vulnerable population. Before accepting life with SARS-CoV-2, challenges remain, especially with regard to communication, the healthcare system, and vaccination. A society-wide strategy involving multiple stakeholders should be adopted to mitigate the damage and achieve a true world where we are "Living with COVID-19".
... According to Taquet et al, non-specific PASC symptomatic shows no clinical excess when compared to other respiratory infections (93). However, its occurrence is more frequent, as COVID-19 incidence is higher compared to other respiratory infections (94). Beside the burden of PASC on the health care system, non-specific PASC has been correlated to reduced working hours and inability to work in 22% of PASC patients (95). ...
The role of autoimmunity in post-acute sequelae of COVID-19 (PASC) is not well explored, although clinicians observe a growing population of convalescent COVID-19 patients with manifestation of post-acute sequelae of COVID-19. We analyzed the immune response in 40 post-acute sequelae of COVID-19 patients with non-specific PASC manifestation and 15 COVID-19 convalescent healthy donors. The phenotyping of lymphocytes showed a significantly higher number of CD8+ T cells expressing the Epstein-Barr virus induced G protein coupled receptor 2, chemokine receptor CXCR3 and C-C chemokine receptor type 5 playing an important role in inflammation and migration in PASC patients compared to controls. Additionally, a stronger, SARS-CoV-2 reactive CD8+ T cell response, characterized by IFNγ production and predominant T EMRA phenotype but low SARS-CoV-2 avidity was detected in PASC patients compared to controls. Furthermore, higher titers of several autoantibodies were detected among PASC patients. Our data suggest that a persistent inflammatory response triggered by SARS-CoV-2 might be responsible for the observed sequelae in PASC patients. These results may have implications on future therapeutic strategies.
... To explore the COVID-19 pandemic, some researchers propose different models to delineate the disease transmission dynamics and assess the course or severity of COVID-19 [7][8][9][10][11][12][13][14]. Hao et al. [15] construct a SAPHIRE model to reconstruct the fullspectrum dynamics of COVID-19 in Wuhan. ...
... The disease-free equilibrium of model (1), given by (12), is locally asymptotically stable whenever R 0 < 1, and unstable if R 0 > 1. ...
The realistic assessments of public health intervention strategies are of great significance to effectively combat the COVID-19 epidemic and the formation of intervention policy. In this paper, an extended COVID-19 epidemic model is devised to assess the severity of the pandemic and explore effective control strategies. The model is characterized by ordinary differential equations with seven-state variables, and it incorporates some parameters associated with the interventions (i.e., media publicity, home isolation, vaccination and face-mask wearing) to investigate the impacts of these interventions on the spread of the COVID-19 epidemic. Some dynamic behaviors of the model, such as forward and backward bifurcation, are analyzed. Specifically, we calibrate the model parameters using actual COVID-19 infected data in Brazil by Markov Chain Monte Carlo algorithm such that we can study the effects of interventions on a practical case. Through a comprehensive exploration of model design and analysis, model calibration, sensitivity analysis, implementation of optimal control problems and cost-effectiveness analysis, the rationality of our model is verified, and the effective strategies to combat the epidemic in Brazil are revealed. The results show that the asymptomatic infected individuals are the main drivers of COVID-19 transmission, and rapid detection of asymptomatic infections is critical to combat the COVID-19 epidemic in Brazil. Interestingly, the effect of the vaccination rate associated with pharmaceutical intervention on the basic reproduction number is much lower than that of non-pharmaceutical interventions (NPIs). Our study also highlights the importance of media publicity. To reduce the infected individuals, the multi-pronged NPIs have considerable positive effects on controlling the outbreak of COVID-19. The infections are significantly decreased by the early implementation of media publicity complemented with home isolation and face-mask wearing strategy. When the cost of implementation is taken into account, the early implementation of media publicity complemented with a face-mask wearing strategy can significantly mitigate the second wave of the epidemic in Brazil. These results provide some management implications for controlling COVID-19.
