Department of Evolutionary Theory, Max Planck Institute for Evolutionary Biology, August-Thienemann-Strasse 2, 24306 Plön, Germany.
J R Soc Interface. 2022 Jun;19(191):20220045. doi: 10.1098/rsif.2022.0045. Epub 2022 Jun 29.
When vaccine supply is limited but population immunization urgent, the allocation of the available doses needs to be carefully considered. One aspect of dose allocation is the time interval between the first and the second injections in two-dose vaccines. By stretching this interval, more individuals can be vaccinated with the first dose more quickly, which can be beneficial in reducing case numbers, provided a single dose is sufficiently effective. On the other hand, there has been concern that intermediate levels of immunity in partially vaccinated individuals may favour the evolution of vaccine escape mutants. In that case, a large fraction of half-vaccinated individuals would pose a risk-but only if they encounter the virus. This raises the question whether there is a conflict between reducing the burden and the risk of vaccine escape evolution or not. We develop an SIR-type model to assess the population-level effects of the timing of the second dose. Trade-offs can occur both if vaccine escape evolution is more likely or if it is less likely in half-vaccinated than in unvaccinated individuals. Their presence or absence depends on the efficacies for susceptibility and transmissibility elicited by a single dose.
当疫苗供应有限但人群免疫需求迫切时，需要仔细考虑可用剂量的分配。剂量分配的一个方面是两剂疫苗中第一针和第二针之间的时间间隔。通过延长这个间隔，可以更快地为更多人接种第一针，这在减少病例数量方面是有益的，前提是单剂疫苗足够有效。另一方面，人们担心部分接种个体的中间免疫水平可能有利于疫苗逃逸突变体的进化。在这种情况下，大量半接种个体将构成风险——但前提是他们接触到病毒。这就提出了一个问题，即减轻负担和疫苗逃逸进化风险之间是否存在冲突。我们开发了一个 SIR 型模型来评估第二针时间对人群水平的影响。如果疫苗逃逸进化的可能性更大，或者半接种个体的疫苗逃逸进化可能性比未接种个体更小，那么就会出现权衡取舍。它们的存在或不存在取决于单剂疫苗引起的易感性和传染性的功效。
