Yu Hongjie's research group has made a series of progress in the field of new coronary pneumonia school closures and vaccine immunization effects

Recently, the research group of Yu Hongjie from the School of Public Health of Fudan University has made a series of progress in the fields of COVID-19 school closure strategy, COVID-19 vaccine protection efficacy and herd immunity research.

1.

The effect of symptom-based school closures on infectious diseases such as seasonal flu has been controversial

This study uses a data-driven approach to model the spread of COVID-19 at the individual level, simulating the reactive school closures in Italy combined with other social distancing policies since the fall of 2020 (i.

Figure 1.

Accordingly, this study proposes an alternative strategy, that is, in addition to symptom-based PCR testing, students are subjected to weekly rapid antigen screening, and once a student is found to be positive, the student's class is suspended for two weeks

This study quantitatively measured the control effect of a symptom monitoring-based school closure strategy on the spread of COVID-19 and its potential influencing factors, and proposed a school closure strategy combined with rapid antigen screening, which can greatly reduce the disease burden of COVID-19.

Liu Quanhui, an associate researcher at the School of Computer Science, Sichuan University, and Zhang Juanjuan, a young researcher at the School of Public Health, Fudan University, are the co-first authors.

2.

A COVID-19 vaccine helps control the spread of SARS-CoV-2, but vaccine-induced protection decays over time

The results of the study showed that the mRNA vaccines of Moderna and Pfizer were 63.

Figure 2.

Dr.

3.

In the context of the global new crown epidemic that has not yet ended and the frequent mutation of the virus, China is facing enormous pressure from overseas imported epidemics to cause local outbreaks and epidemics

This study assessed whether the current vaccination strategy in China could achieve herd immunity against the Delta variant if the COVID-19 epidemic was introduced on December 1, 2021 by constructing a model of the transmission dynamics of COVID-19; if not, how to optimize the prevention and control strategy to increase the likelihood of achieving herd immunity
.
The results of the study show that when the protective effect (VE) of the new crown vaccine against Delta variant infection is 54.
3%, China's current vaccination strategy (Strategy 1: give priority to people over 12 years old, and start from November 1, 2021).
Expanded to people over 3 years old) cannot establish herd immunity on December 1, 2021, but can significantly reduce the burden of disease (about 50% reduction in the number of infected people)
.
Herd immunity cannot be established if all people over 3 years of age are vaccinated (Strategy 2) at the start of the vaccination program (Figure 3)
.
The study further assessed the impact of delaying the introduction of the outbreak and taking different intensities of non-pharmaceutical interventions (NPIs) on the spread of SARS-CoV-2
.
Assuming that the epidemic is introduced into China between December 2021 and February 2022, and maintaining moderate-intensity NPIs (effective reproduction number of 1.
5 to 2.
0), both strategies can effectively block the spread of the virus
.

Figure 3.
Vaccine coverage, daily incidence, number of effective reproductions, and population immunity levels over time

In addition, the article also estimated the herd immunity threshold under different VE of the new crown vaccine (Figure 4)
.
It was found that if the VE is less than 85%, even if the vaccine coverage reaches 100%, it is impossible to establish herd immunity against the Delta variant
.
Improving vaccine coverage and VE at the same time is the only potentially feasible approach
.
For example, with a vaccine with VE=90%, herd immunity can only be achieved when the vaccination rate exceeds 93%
.

Figure 4.
Herd immunity thresholds under different VEs of the new crown vaccine

This study quantitatively measured the effect of vaccine-induced immunity levels on the spread of COVID-19 in the population
.
Against the background of frequent occurrence of mutants with stronger transmission ability and immune evasion ability, it is a big challenge to achieve herd immunity
.
Strategies such as increasing vaccination rates, developing better vaccines for VE, or boosting immunization with a third dose are the keys to achieving herd immunity against mutant strains
.
Before the establishment of herd immunity, NPIs still need to be applied to prevent the outbreak and epidemic of new coronary pneumonia
.

Postdoctoral fellow Liu Hengcong and young researcher Zhang Juanjuan of the School of Public Health of Fudan University are the co-first authors, and Professor Yu Hongjie of the School of Public Health of Fudan University is the corresponding author
.

The above three studies were funded by the National Natural Science Foundation of China (82130093) and other projects
.