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. 2022 Oct 3;5(10):e2236670.
doi: 10.1001/jamanetworkopen.2022.36670.

Estimated Protection of Prior SARS-CoV-2 Infection Against Reinfection With the Omicron Variant Among Messenger RNA-Vaccinated and Nonvaccinated Individuals in Quebec, Canada

Affiliations

Estimated Protection of Prior SARS-CoV-2 Infection Against Reinfection With the Omicron Variant Among Messenger RNA-Vaccinated and Nonvaccinated Individuals in Quebec, Canada

Sara Carazo et al. JAMA Netw Open. .

Abstract

Importance: 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.

Objective: 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.

Exposures: Prior laboratory-confirmed SARS-CoV-2 infection with or without mRNA vaccination.

Main outcomes and measures: 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.

Results: 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.

Conclusions and relevance: 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.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Skowronski reported receiving grants from the Public Health Agency of Canada, the Michael Smith Foundation for Health Research, the Canadian Institutes of Health Research, and the British Columbia Centre for Disease Control Foundation paid to her institution and unrelated to the current work. Dr Sauvageau reported receiving grants from the Québec Ministry of Health and Social Services during the conduct of the study. Dr R. Gilca reported receiving personal fees (honoraria) from AbbVie for a conference on respiratory syncytial virus burden in children outside the submitted work. Dr Fafard reported receiving grants from the Ministry of Health of Quebec and the Canadian COVID Genomics Network for sequencing of positive SARS-CoV-2 samples outside the submitted work and serving as chair of the Institut National de Santé Publique du Québec provincial SARS-CoV-2 genomic surveillance committee. Dr De Serres reported receiving a grant from Pfizer for a meningococcal B antibody seroprevalence study unrelated to the current work. No other disclosures were reported.

Figures

Figure.
Figure.. Prior SARS-CoV-2 Infection and Messenger RNA Vaccine Effectiveness Against Omicron Reinfection in Quebec, Canada, by Number of Doses and Timing
Logistic regression models compared vaccinated and unvaccinated persons with prior infection (PI) with unvaccinated individuals without PI. All estimates were adjusted for age (12-17, 18-49, 50-69, and ≥70 years), sex, testing indication, and epidemiologic week. PI-NV indicates prior infection, nonvaccinated; PI-V1, PI-V2, or PI-V3, prior infection before 1, 2, or 3 vaccine doses, respectively; V1-PI, prior infection after 1 vaccine dose; V1-PI-V2, prior infection after the first but before the second vaccine dose; V1-PI-V3, prior infection after the first but before the second and third vaccine doses; V2-PI, prior infection after 2 vaccine doses; V2-PI-V3, prior infection after the second but before the third vaccine dose. Error bars indicate 95% CIs.

References

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