报告题目： Modelling COVID-19 Vaccine Breakthrough Infections in Highly Vaccinated Israel-the effects of waning immunity and third vaccination dose

报告人：香港理工大学应用数学系 Professor Daihai He（何岱海）

报告时间：2022年3月25号（周五1:30-2:30）

腾讯会议：761462921

密码： 123456

摘要：In August 2021, a major wave of the SARS-CoV-2 Delta variant erupted in the highly vaccinated population of Israel. The Delta variant has a transmission advantage over the Alpha variant, and thus replaced it in approximately two months. The outbreak led to an unexpectedly large proportion of breakthrough infections (BTI)-- a phenomenon that received worldwide attention. The BTI proportion amongst cases in the age group of 60+ years reached levels as high as ∼85% in August 2021. Most of the Israeli population, especially those 60+ age, received their second dose of the vaccination, four months before the invasion of the Delta variant. Hence, either the vaccine induced immunity dropped significantly or the Delta variant possesses immunity escaping abilities. In this work, we analyzed and model age-structured cases, vaccination coverage, and vaccine BTI data obtained from the Israeli Ministry of Health, to help understand the epidemiological factors involved in the outbreak. We propose a mathematical model which captures a multitude of factors, including age structure, the time varying vaccine efficacy, time varying transmission rate, BTIs, reduced susceptibility and infectivity of vaccinated individuals, protection duration of the vaccine induced immunity, and the vaccine distribution. We fitted our model to the cases among vaccinated and unvaccinated, for <60 and 60+ age groups, to address the aforementioned factors. We found that the transmission rate was driven by multiple factors including the invasion of Delta variant and the mitigation measures. Through a model reconstruction of the reproductive number R0(t), it was found that the peak transmission rate of the Delta variant was 1.96 times larger than the previous Alpha variant. The model estimated that the vaccine efficacy dropped significantly from >90% to ∼40% over 6 months, and that the immunity protection duration has a peaked Gamma distribution (rather than exponential). We further performed model simulations quantifying the important role of the third vaccination booster dose in reducing the levels of breakthrough infections. This allowed us to explore “what if” scenarios should the booster not have been rolled out. Application of this framework upon invasion of new pathogens, or variants of concern, can help elucidate important factors in the outbreak dynamics and highlight potential routes of action to mitigate their spread.

报告人简介：何岱海，西安交通大学博士、加拿大麦克马斯特大学博士，曾在北京师范大学、美国密歇根大学、以色列特拉维夫大学等校做博士后研究，2012年至今在香港理工大学工作，博士生导师，主要从事生物数学与流行病学领域的研究，获得香港研究资助局项目、香港食品与卫生环境署健康与医疗项目等多项基金资助。曾获国际疾病监测学会2018年度科学贡献最佳论文第二名。近年来在新发突发以及重要传染病的流行病学研究、传播动力学研究及相关政策评估方面做出了很多系统和开创性的探索，是该领域的杰出青年学者，其关于2009年大流行流感和2015年寨卡病毒的研究结果被国内外媒体广泛报道。近年来（2009年至今）已发表文章60余篇。