Kayano Taishi, Sasanami Misaki, Nishiura Hiroshi
Kyoto University School of Public Health, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
Center for Health Security, Kyoto University Graduate School of Medicine, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
Vaccine X. 2024 Aug 12;20:100547. doi: 10.1016/j.jvacx.2024.100547. eCollection 2024 Oct.
Stringent public health and social measures against COVID-19 infection were implemented to avoid an overwhelming hospital caseload and excessive number of deaths, especially among elderly people. We analyzed population-level immunity and predicted mortality, calculated as the potential number of deaths on a given calendar date in Japan, to develop a science-based exit strategy from stringent control measures.
Immune proportions were inferred by age group using vaccination coverage data and the estimated number of naturally infected individuals. Immunity against symptomatic illness and death were estimated separately, allowing for inference of the immune fraction that was protected against either COVID-19-related symptomatic infection or death. By multiplying the infection fatality risk by age group for the immune fraction, the potential number of deaths was obtained.
Accounting for a second and third dose of messenger RNA vaccine in the present-day population, approximately 155,000 potential deaths would be expected among people aged ≥ 60 years if all individuals were infected at the very end of 2022. A fourth dose (i.e., second booster) with a coverage identical to that of the third dose could reduce mortality by 60%. In all examined settings, the largest number of deaths occurred among people aged 80 years and older.
Our estimates can help policymakers understand the mortality impact of the COVID-19 epidemic in a quantitative manner and the critical importance of timely immunization so as to assist in decision making.
为避免医院不堪重负和大量死亡，尤其是老年人死亡，针对新冠病毒感染实施了严格的公共卫生和社会措施。我们分析了人群层面的免疫力并预测了死亡率（以日本给定日历日期的潜在死亡人数计算），以制定基于科学的从严格管控措施中退出的策略。
利用疫苗接种覆盖率数据和估计的自然感染个体数量，按年龄组推断免疫比例。分别估计针对有症状疾病和死亡的免疫力，从而推断出对新冠病毒相关有症状感染或死亡具有保护作用的免疫比例。通过将各年龄组的感染致死风险乘以免疫比例，得出潜在死亡人数。
考虑到当前人群中接种的第二剂和第三剂信使核糖核酸疫苗，如果所有个体在2022年底全部感染，预计60岁及以上人群中约有15.5万人可能死亡。第四剂（即第二次加强针）接种覆盖率与第三剂相同时，可将死亡率降低60%。在所有研究的情况下，死亡人数最多的是80岁及以上人群。
我们的估计有助于政策制定者以定量方式了解新冠疫情对死亡率的影响以及及时免疫的至关重要性，从而辅助决策。
