EFFICACY of NATURAL IMMUNITY AGAINST REINFECTION with SARS-CoV-2 B.1.351 VARIANT

ABSTRACT

Background: Reinfections with emerging SARS-CoV-2 variants are a serious concern. This study estimated the efficacy of immunity induced by natural infection against reinfection with B.1.351 and B.1.1.7 variants. Methods: Two retrospective matched cohort studies were conducted in Qatar from March 8-April 21 to assess reinfection in the national cohort of individuals with a prior PCR-confirmed infection and the national cohort of antibody-positive individuals, matching each in a 11 ratio by demographic characteristics to the national cohort of antibody-negative individuals. Incidence risks (using the Kaplan-Meier estimator), incidence rates, and efficacy of natural infection against reinfection were estimated. Results: In the study comparing 44,821 individuals with a prior PCR-confirmed infection to antibody-negative individuals, the efficacy of natural infection against reinfection was 92.3% (95% CI 90.3-93.8%) for B.1.351, 97.6% (95% CI 95.7-98.7%) for B.1.1.7, and 87.9% (95% CI 84.7-90.5%) for unidentified variants (mostly suspected B.1.351 cases based on weekly sequencing analysis). In the second study, comparing 20,406 antibody-positive to antibody-negative individuals, efficacy was 86.4% (95% CI 82.5-89.5%) for B.1.351, 96.4% (95% CI 92.1-98.3%) for B.1.1.7, and 83.1% (95% CI 77.2-87.5%) for unidentified variants. Additional analyses and sensitivity analyses confirmed these results, albeit with slightly lower efficacies. Conclusion: Natural infection with SARS-CoV-2 induces robust protection of 80-90% against reinfection with B.1.351 even a year after the primary infection, but lower than that against B.1.1.7.