Adaptive behaviors and vaccination on curbing COVID-19 transmission: Modeling simulations in eight countries.

Current persistent outbreak of COVID-19 is triggering a series of collective responses to avoid infection. To further clarify the impact mechanism of adaptive protection behavior and vaccination, we developed a new transmission model via a delay differential system, which parameterized the roles of adaptive behaviors and vaccination, and allowed to simulate the dynamic infection process among people. By validating the model with surveillance data during March 2020 and October 2021 in America, India, South Africa, Philippines, Brazil, UK, Spain and Germany, we quantified the protection effect of adaptive behaviors by different forms of activity function. The modeling results indicated that (1) the adaptive activity function can be used as a good indicator for fitting the intervention outcome, which exhibited short-term awareness in these countries, and it could reduce the total human infections by 3.68, 26.16, 15.23, 4.23, 7.26, 1.65, 5.51 and 7.07 times, compared with the reporting; (2) for complete prevention, the average proportions of people with immunity should be larger than 90%, 92%, 86%, 71%, 92%, 84%, 82% and 76% with adaptive protection behaviors, or 91%, 97%, 94%, 77%, 92%, 88%, 85% and 90% without protection behaviors; and (3) the required proportion of humans being vaccinated is a sub-linear decreasing function of vaccine efficiency, with small heterogeneity in different countries. This manuscript was submitted as part of a theme issue on "Modelling COVID-19 and Preparedness for Future Pandemics".

Transmission trends of the global COVID-19 pandemic with combined effects of adaptive behaviours and vaccination.

We developed a mechanism model which allows for simulating the novel coronavirus (COVID-19) transmission dynamics with the combined effects of human adaptive behaviours and vaccination, aiming at predicting the end time of COVID-19 infection in global scale. Based on the surveillance information (reported cases and vaccination data) between 22 January 2020 and 18 July 2022, we validated the model by Markov Chain Monte Carlo (MCMC) fitting method. We found that (1) if without adaptive behaviours, the epidemic could sweep the world in 2022 and 2023, causing 3.098 billion of human infections, which is 5.39 times of current number; (2) 645 million people could be avoided from infection due to vaccination; and (3) in current scenarios of protective behaviours and vaccination, infection cases would increase slowly, levelling off around 2023, and it would end completely in June 2025, causing 1.024 billion infections, with 12.5 million death. Our findings suggest that vaccination and the collective protection behaviour remain the key determinants against the global process of COVID-19 transmission.

Refocus on Immunogenic Characteristics of Convalescent COVID-19 Challenged by Prototype SARS-CoV-2.

Background: Mass basic and booster immunization programs effectively contained the spread of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus, also known as COVID-19. However, the emerging Variants of Concern (VOCs) of COVID-19 evade the immune protection of the vaccine and increase the risk of reinfection. Methods: Serum antibodies of 384 COVID-19 cases recovered from SARS-CoV-2 infection were examined. Correlations between clinical symptoms and antibodies against VOCs were analyzed. Result: All 384 cases (aged 43, range 1−90) were from 15 cities of Guangdong, China. The specific IgA, IgG, and IgM antibodies could be detected within 4−6 weeks after infection. A broad cross-reaction between SARS-CoV-2 and Severe Acute Respiratory Syndrome Coronavirus, but not with Middle East Respiratory Syndrome Coronavirus was found. The titers of neutralization antibodies (NAbs) were significantly correlated with IgG (r = 0.667, p < 0.001), but showed poor neutralizing effects against VOCs. Age, fever, and hormone therapy were independent risk factors for NAbs titers reduction against VOCs. Conclusion: Humoral immunity antibodies from the original strain of COVID-19 showed weak neutralization effects against VOCs, and decreased neutralizing ability was associated with initial age, fever, and hormone therapy, which hindered the effects of the COVID-19 vaccine developed from the SARS-CoV-2 prototype virus.

Vaccination against Varicella Zoster Virus Infection in Less Developed Regions of Guangdong, China: A Cross-Sectional Serosurveillance Study.

Vaccination is the key to prevent varicella zoster virus (VZV) infection in children. Voluntary and self-funded strategies have led to variable vaccination rates against VZV in China. For low-income populations, in particular, the effects of VZV vaccination have been insufficiently estimated. Community-based serosurveillance was conducted in two less developed regions, Zhanjiang and Heyuan, of Guangdong, China. Anti-VZV IgG antibodies in serum were detected by ELISA. The vaccination data were derived from the Guangdong Immune Planning Information System. A total of 4221 participants were involved, of which 3377 were from three counties of Zhanjiang and the other 844 were from one county of Heyuan, Guangdong, China. The total VZV IgG seropositivity rate in vaccinated individuals was 34.30% and 42.76%, while it was 89.61% and 91.62% in non-vaccinated populations of Zhanjiang and Heyuan, respectively. The seropositivity rate increased gradually with age, reaching ~90% in the >20- to 30-year-old group. The VarV vaccination rates of children aged 1-14 years were 60.47% for one dose and 6.20% for two doses in Zhanjiang, and 52.24% for one dose and 4.48% for two doses in Heyuan. Compared with the non-vaccinated group (31.19%) and one-dose group (35.47%), the positivity rate of anti-VZV IgG antibodies was significantly higher in the two-dose group (67.86%). Before the VarV policy was reformed, the anti-VZV IgG positivity rate was 27.85% in the one-dose-vaccinated participants, which increased to 30.43% after October 2017. The high seroprevalence in participants was due to infection of VZV in Zhanjiang and Heyuan, not vaccination against VZV. Children aged 0-5 years are still vulnerable to varicella, so a two-dose vaccination program should be implemented to prevent onward transmission of VZV.