THURSDAY, Dec. 16, 2021 (HealthDay News) — Natural immunity protects against reinfection with the alpha and beta variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), according to a study published online Dec. 15 in the New England Journal of Medicine.

Hiam Chemaitelly, Ph.D., from Weill Cornell Medicine-Qatar in Doha, and colleagues estimated the efficacy of immunity induced by natural infection against reinfection by comparing the incidence of SARS-CoV-2 reinfection in a cohort of persons who had previous confirmed infection before Jan. 1, 2021, with incidence in a cohort of antibody-negative individuals with no evidence of previous infection using data from national databases in Qatar. Participants were followed from March 8 to April 21, 2021.

The researchers found that at 42 days of follow-up, the cumulative incidence was 0.27 and 3.44 percent in the previous-infection cohort and antibody-negative cohort, respectively, for the beta variant, and was 0.03 and 1.35 percent, respectively, for the alpha variant. The incidence rates of infection with the beta variant were estimated at 4.34 and 56.25 cases per 10,000 person-weeks in the previous infection and antibody-negative cohorts, respectively; for the alpha variant, the corresponding incidence rates were 0.53 and 22.44 cases per 10,000 person-weeks. The efficacy of natural infection against reinfection was estimated at 92.3 and 97.6 percent for the beta and alpha variants, respectively.

“These findings give some insights into the hypothesis that natural immunity may provide protection against known variants of concern,” the authors write.

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