Yu Hongjie's research group has made a series of progress in the fields of global diversity of new crown vaccination and disease burden caused by Delta strains

Recently, the research group of Yu Hongjie from Fudan University has made a series of progress in the field of the diversity of global new crown vaccination and the epidemic disease burden caused by the import of Delta variant strains into China.

1.

Since December 2020, large-scale vaccination of the new crown vaccine has been carried out around the world.

The results showed that adenovirus vector vaccines, mRNA vaccines, inactivated vaccines, protein subunit vaccines and conjugate vaccines were administered in 180, 159, 116, 10 and 3 countries, respectively

Figure 1.

This study quantitatively characterizes the policies, vaccination rates, and needs of COVID-19 vaccination in various countries around the world, reveals the inequity and imbalance of vaccination at this stage, and suggests that low vaccination rates in some countries may hinder the control of the COVID-19 pandemic

School of Public Health, Fudan University 2020 master student Chen Zhiyuan, 2019 direct doctoral student Zheng Wen, 2020 doctoral student Wu Qianhui, 2019 master student Chen Xinghui and 2020 doctoral student Peng Jue are the co-first authors, professor of School of Public Health, Fudan University, Shanghai The Municipal Institute of Major Infectious Diseases and Biosafety and the Department of Infectious Diseases, Huashan Hospital Affiliated to Fudan University, both hired PI Yu Hongjie as the corresponding author

2.

The new coronavirus (SARS-CoV-2) Delta variant was discovered in India in October 2020

After China successfully controlled the Wuhan epidemic in early 2020, it continued to face the risk of local outbreaks caused by overseas imports.

To this end, Yu Hongjie's research group constructed a stochastic susceptibility-infection-recovery (SIR) transmission dynamics model, based on China's demographic characteristics, population contact patterns, the basic reproduction number and virulence of the Delta variant, the current status of vaccination, and targeting of variant strains.

The baseline scenario of the model assumes that 40 cases of Delta variant infection are imported overseas on December 1, 2021

Under the "adult+adolescent" vaccination strategy, the incidence of symptomatic cases, hospitalization, ICU admission and death in the whole population caused by the epidemic of the Delta variant was 439/1000 (95%CI: 415-447/1000), 27/1000 (95%CI: 415-447/1000).

Figure 2.

(A) Incidence of symptomatic cases; (B) Hospitalization rate; (C) Incidence of ICU admission; (D) Mortality rate

In contrast, the "adult+adolescent+child" vaccination strategy, which expanded vaccination to 3-11-year-olds, significantly reduced symptomatic infections (39%) and hospitalizations (68%) in this age group, but not enough to prevent virus transmission, with little impact on disease burden in other age groups (Figure 2)

Figure 3.
Rate ratios of infection, hospitalization, ICU admission, and death among symptomatic cases with the Delta variant

NV: no vaccination; AA: "adult + adolescent" vaccination strategy; AAC: "adult + adolescent + child" vaccination strategy

Regardless of the strategy, vaccination reduces the risk of morbidity and serious clinical outcomes
.
In terms of age groups, the incidence of symptomatic cases, hospitalization, ICU admission and death in the unvaccinated population was 0.
9-1.
4 times, 2.
0-3.
1 times, 2.
1-3.
3 times, and 2.
1-3.
3 times that of the vaccinated population, respectively (Fig.
2)
.

This study further simulated the impact of improving the protective efficacy of the new crown vaccine and adopting non-drug interventions on the disease burden
.
The better the protective effect of the vaccine against Delta variant infection, the lower the intensity of non-drug interventions required to control the disease burden to a lower level, and the more conducive to restoring normal social life order
.
Under the "adult+adolescent+child" vaccination strategy, when the protective effect of the vaccine exceeds 88%, even if no non-drug intervention measures are taken, the number of deaths caused by the epidemic of the Delta variant strain can be controlled to be lower than that of the seasonal influenza epidemic in China The annual level of excess respiratory disease deaths (88,100)
.

In summary, considering the higher transmissibility and virulence of the Delta variant and the lower protective effect of the vaccine on it, although there is a high vaccine coverage rate for people ≥12 years old in China, once the Delta variant becomes popular in China , will still cause a severe disease burden
.
The results of the study support the expansion of the target population for vaccination to 3-11 years old in China, so as to avoid the disease burden being tilted towards this age group ; and it is emphasized that non-drug interventions of a certain intensity should be maintained , immunization should be rapidly promoted , and active research and development should be carried out to better protect the effect.
vaccine in response to the epidemic of variant strains with higher transmissibility, pathogenicity and virulence .

Cai Jun, a postdoctoral fellow at the School of Public Health, Fudan University, and Associate Professor Yang Juan, from the School of Public Health, Fudan University, and Shanghai Institute of Major Infectious Diseases and Biosafety are the co-first authors.
The hospital and the Department of Infectious Diseases, Huashan Hospital Affiliated to Fudan University, both employ PI Yu Hongjie as the corresponding author
.

The above research was supported by the National Natural Science Foundation of China (82130093), the National Key Research and Development Program (2021YFC0863400) and the Shanghai Municipal Science and Technology Major Project (ZD2021CY001)
.