Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
Department of Epidemiology, Johns Hopkins University, Baltimore, Maryland, United States of America.
PLoS One. 2024 Feb 23;19(2):e0299304. doi: 10.1371/journal.pone.0299304. eCollection 2024.
Evidence on protection of different patterns of infection- and vaccine-acquired immunity against Omicron-associated severe illness is useful in planning booster vaccination strategies. We examined protection of prior SARS-CoV-2 infection, a third or a fourth COVID-19 vaccine dose, and hybrid immunity against Omicron-associated severe illness.
This population-based cohort study followed five million individuals with at least one SARS-CoV-2 RT-PCR test before November 21, 2021 until an Omicron-associatedhospitalization or death. We used Cox regression models to estimate risks of Omicron-associated hospitalization and a composite severe outcome (hospitalized and death), among individuals with infection- and/or vaccination-acquired immunity. Individuals who were unvaccinated and had no history of a prior infection severed as the reference group. Both adjusted hazard ratios (HR) and corresponding protection (one minus adjusted HR), with 95% confidence intervals (CIs), were reported. Three doses provided 94% (95%CI 93-95) and 93% (95%CI 91-94) protection against Omicron-associated hospitalization at 2-3 and ≥3 months post-vaccination respectively, similar to the protection conferred by three doses and a prior infection (2-3 months: 99%, 95%CI 97-100; ≥3 months: 97%, 95%CI 92-99) and four doses (1 month: 87%, 95%CI 79-92; 1-2 months: 96%, 95%CI 92-98). In individuals ≥65 years old, protection of four doses increased to 95% (95%CI 91-98) at 1-2 months, significantly higher than that of three doses over the follow-up period. Similar results were observed with the composite severe outcome.
At least three antigenic exposures, achieved by vaccination or infection, confers significant protection against Omicron-associated hospitalization and death in all age groups. Our findings support a third dose for the overall population, regardless of prior infection status, and a fourth dose for the elderly to maintain high level of immunity and substantially reduce risk of severe illness at individual level.
针对奥密克戎相关重症，不同模式的感染和疫苗获得性免疫的保护作用的相关证据，对于制定加强针接种策略很有帮助。本研究旨在评估既往 SARS-CoV-2 感染、第三或第四剂 COVID-19 疫苗接种以及混合免疫对奥密克戎相关重症的保护作用。
本基于人群的队列研究纳入了 2021 年 11 月 21 日之前至少接受过一次 SARS-CoV-2 RT-PCR 检测的 500 万名个体，随访终点为奥密克戎相关住院或死亡。我们使用 Cox 回归模型来估计具有感染和/或疫苗获得性免疫个体的奥密克戎相关住院和复合严重结局（住院和死亡）的风险。未接种疫苗且无既往感染史的个体作为参照组。报告了调整后的风险比（HR）和相应的保护率（调整后 HR 的 1 减数值，95%置信区间（CI））。第三剂疫苗在接种后 2-3 个月和≥3 个月时，对奥密克戎相关住院的保护率分别为 94%（95%CI 93-95）和 93%（95%CI 91-94），与第三剂疫苗和既往感染（2-3 个月：99%，95%CI 97-100；≥3 个月：97%，95%CI 92-99）和第四剂疫苗（1 个月：87%，95%CI 79-92；1-2 个月：96%，95%CI 92-98）的保护作用相似。在≥65 岁的个体中，第四剂疫苗在 1-2 个月时的保护率增加到 95%（95%CI 91-98），显著高于整个随访期间第三剂疫苗的保护率。对于复合严重结局，也观察到了类似的结果。
在所有年龄段，至少三次抗原暴露（通过接种或感染获得）可显著降低奥密克戎相关住院和死亡的风险。本研究结果支持在全人群中接种第三剂疫苗，无论既往感染状态如何，以及为了在个体层面保持高水平免疫并显著降低重症风险，为老年人接种第四剂疫苗。
