Biological Risks Unit, Institut National de Santé Publique du Québec, Quebec City, Quebec, Canada.
Communicable Diseases and Immunization Services, British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
JAMA Netw Open. 2022 Oct 3;5(10):e2236670. doi: 10.1001/jamanetworkopen.2022.36670.
The Omicron variant is phylogenetically and antigenically distinct from earlier SARS-CoV-2 variants and the original vaccine strain. Protection conferred by prior SARS-CoV-2 infection against Omicron reinfection, with and without vaccination, requires quantification.
To estimate the protection against Omicron reinfection and hospitalization conferred by prior heterologous non-Omicron SARS-CoV-2 infection and/or up to 3 doses of an ancestral, Wuhan-like messenger RNA (mRNA) vaccine.
DESIGN, SETTING, AND PARTICIPANTS: This test-negative, population-based case-control study was conducted between December 26, 2021, and March 12, 2022, and included community-dwelling individuals aged 12 years or older who were tested for SARS-CoV-2 infection in the province of Quebec, Canada.
Prior laboratory-confirmed SARS-CoV-2 infection with or without mRNA vaccination.
The main outcome was laboratory-confirmed SARS-CoV-2 reinfection and associated hospitalization, presumed to be associated with the Omicron variant according to genomic surveillance. The odds of prior infection with or without vaccination were compared for case participants with Omicron infection and associated hospitalizations vs test-negative control participants. Estimated protection was derived as 1 - the odds ratio, adjusted for age, sex, testing indication, and epidemiologic week. Analyses were stratified by severity and time since last non-Omicron infection or vaccine dose.
This study included 696 439 individuals (224 007 case participants and 472 432 control participants); 62.2% and 63.9% were female and 87.4% and 75.5% were aged 18 to 69 years, respectively. Prior non-Omicron SARS-CoV-2 infection was detected for 9505 case participants (4.2%) and 29 712 control participants (6.3%). Among nonvaccinated individuals, prior non-Omicron infection was associated with a 44% reduction (95% CI, 38%-48%) in Omicron reinfection risk, which decreased from 66% (95% CI, 57%-73%) at 3 to 5 months to 35% (95% CI, 21%-47%) at 9 to 11 months postinfection and was below 30% thereafter. The more severe the prior infection, the greater the risk reduction. Estimated protection (95% CI) against Omicron infection was consistently significantly higher among vaccinated individuals with prior infection compared with vaccinated infection-naive individuals, with 65% (63%-67%) vs 20% (16%-24%) for 1 dose, 68% (67%-70%) vs 42% (41%-44%) for 2 doses, and 83% (81%-84%) vs 73% (72%-73%) for 3 doses. For individuals with prior infection, estimated protection (95% CI) against Omicron-associated hospitalization was 81% (66%-89%) and increased to 86% (77%-99%) with 1, 94% (91%-96%) with 2, and 97% (94%-99%) with 3 mRNA vaccine doses, without signs of waning.
The findings of this study suggest that vaccination with 2 or 3 mRNA vaccine doses among individuals with prior heterologous SARS-CoV-2 infection provided the greatest protection against Omicron-associated hospitalization. In the context of program goals to prevent severe outcomes and preserve health care system capacity, a third mRNA vaccine dose may add limited protection in twice-vaccinated individuals with prior SARS-CoV-2 infection.
奥密克戎变异株在进化和抗原上与早期 SARS-CoV-2 变异株和原始疫苗株不同。先前 SARS-CoV-2 感染对奥密克戎再感染的保护作用，无论是否接种疫苗，都需要进行量化。
估计先前异源非奥密克戎 SARS-CoV-2 感染和/或最多 3 剂原始、武汉样信使 RNA（mRNA）疫苗对奥密克戎再感染和住院的保护作用。
设计、地点和参与者：这是一项基于阴性对照的病例对照研究，于 2021 年 12 月 26 日至 2022 年 3 月 12 日期间在加拿大魁北克省进行，纳入了年龄在 12 岁及以上的社区居住者，他们在该省接受了 SARS-CoV-2 感染检测。
先前实验室确认的 SARS-CoV-2 感染，无论是否接种了 mRNA 疫苗。
主要结果是实验室确认的 SARS-CoV-2 再感染和相关住院，根据基因组监测，假定与奥密克戎变异株有关。奥密克戎感染和相关住院的病例参与者与阴性对照参与者相比，比较了有或无疫苗接种的先前感染的可能性。估计的保护作用是 1 - 调整年龄、性别、检测指征和流行病学周后的比值比。分析按严重程度和上次非奥密克戎感染或疫苗接种剂量的时间进行分层。
这项研究包括 696439 人（224007 例病例参与者和 472432 例对照参与者）；分别有 62.2%和 63.9%为女性，87.4%和 75.5%年龄在 18 至 69 岁之间。9505 例病例参与者（4.2%）和 29712 例对照参与者（6.3%）检测到先前的非奥密克戎 SARS-CoV-2 感染。在未接种疫苗的个体中，先前的非奥密克戎感染与奥密克戎再感染风险降低 44%（95%CI，38%-48%）相关，从感染后 3 至 5 个月的 66%（95%CI，57%-73%）降至 9 至 11 个月的 35%（95%CI，21%-47%），此后风险低于 30%。先前感染越严重，风险降低幅度越大。与接种疫苗但未感染的个体相比，接种疫苗且有先前感染的个体对奥密克戎感染的估计保护作用（95%CI）一直显著更高，1 剂为 65%（63%-67%），2 剂为 68%（67%-70%），3 剂为 83%（81%-84%），而接种疫苗且未感染的个体为 20%（16%-24%）、42%（41%-44%）和 73%（72%-73%）。对于有先前感染的个体，奥密克戎相关住院的估计保护作用（95%CI）为 81%（66%-89%），增加至 1 剂 86%（77%-99%），2 剂 94%（91%-96%），3 剂 97%（94%-99%），无衰减迹象。
这项研究的结果表明，在先前存在异源 SARS-CoV-2 感染的个体中接种 2 剂或 3 剂 mRNA 疫苗，对奥密克戎相关住院提供了最大的保护。在预防严重后果和维持医疗保健系统能力的项目目标背景下，在先前感染 SARS-CoV-2 并接种过 2 剂疫苗的个体中，第三次 mRNA 疫苗接种可能提供有限的保护作用。
