Data_Sheet_5_Herd Immunity to Ebolaviruses Is Not a Realistic Target for Current Vaccination Strategies.PDF

The recent West African Ebola virus pandemic, which affected >28,000 individuals increased interest in anti-Ebolavirus vaccination programs. Here, we systematically analyzed the requirements for a prophylactic vaccination program based on the basic reproductive number (R0, i.e., the number of secondary cases that result from an individual infection). Published R0 values were determined by systematic literature research and ranged from 0.37 to 20. R0s ≥ 4 realistically reflected the critical early outbreak phases and superspreading events. Based on the R0, the herd immunity threshold (Ic) was calculated using the equation Ic = 1 − (1/R0). The critical vaccination coverage (Vc) needed to provide herd immunity was determined by including the vaccine effectiveness (E) using the equation Vc = Ic/E. At an R0 of 4, the Ic is 75% and at an E of 90%, more than 80% of a population need to be vaccinated to establish herd immunity. Such vaccination rates are currently unrealistic because of resistance against vaccinations, financial/logistical challenges, and a lack of vaccines that provide long-term protection against all human-pathogenic Ebolaviruses. Hence, outbreak management will for the foreseeable future depend on surveillance and case isolation. Clinical vaccine candidates are only available for Ebola viruses. Their use will need to be focused on health-care workers, potentially in combination with ring vaccination approaches.

近年来，累计感染超28000人的西非埃博拉病毒全球大流行，推动了抗埃博拉病毒疫苗接种计划的研究与应用关注。本研究系统分析了基于基本再生数（basic reproductive number, R0，即单一个体感染引发的二代病例数）的预防性疫苗接种计划的必要条件。通过系统文献调研获取的已发表R0值范围为0.37至20。其中R0≥4的场景可真实反映暴发早期的关键阶段与超级传播事件。基于R0，可通过公式Ic=1−(1/R0)计算群体免疫阈值（herd immunity threshold, Ic）；结合疫苗有效性（vaccine effectiveness, E），通过公式Vc=Ic/E可确定实现群体免疫所需的临界疫苗接种覆盖率（critical vaccination coverage, Vc）。当R0为4时，Ic为75%；若疫苗有效性为90%，则需为超80%的人群接种疫苗方可建立群体免疫。鉴于疫苗接种阻力、资金与后勤保障难题，以及缺乏可对所有人类致病埃博拉病毒提供长期保护的疫苗，当前此类接种率尚不切实际。因此，在可预见的未来，疫情暴发管控仍将依赖监测与病例隔离措施。目前仅埃博拉病毒拥有临床候选疫苗，其应用需优先面向医护人员，或可结合环形疫苗接种策略实施。