Chemaitelly et al.: Natural immunity wins again! Duration of immune protection of SARS-CoV-2 natural infection against reinfection in Qatar, 2022, pre-print; 97% PROTECTION on re-infection

by Paul Alexander

Effectiveness of primary infection against severe, critical, or fatal COVID-19 reinfection was 97.3% (95% CI: 94.9-98.6%), irrespective of the variant of primary infection or reinfection, and with no

SOURCE:

Duration of immune protection of SARS-CoV-2 natural infection against reinfection in Qatar, Chemaitelly, 2022

Researchers studied the duration of protection afforded by natural infection, the effect of viral immune evasion on duration of protection, and protection against severe reinfection, in Qatar, between February 28, 2020 and June 5, 2022. They conducted and included three national, matched, retrospective cohort studies so as to compare incidence of SARS-CoV-2 infection and COVID-19 severity among unvaccinated persons with a documented SARS-CoV-2 primary infection, to incidence among those infection-naive and unvaccinated. 

They found that “effectiveness of pre-Omicron primary infection against pre-Omicron reinfection was 85.5% (95% CI: 84.8-86.2%). Effectiveness peaked at 90.5% (95% CI: 88.4-92.3%) in the 7th month after the primary infection, but waned to ~70% by the 16th month. Extrapolating this waning trend using a Gompertz curve suggested an effectiveness of 50% in the 22nd month and <10% by the 32nd month. Effectiveness of pre-Omicron primary infection against Omicron reinfection was 38.1% (95% CI: 36.3-39.8%) and declined with time since primary infection. A Gompertz curve suggested an effectiveness of <10% by the 15th month. Effectiveness of primary infection against severe, critical, or fatal COVID-19 reinfection was 97.3% (95% CI: 94.9-98.6%), irrespective of the variant of primary infection or reinfection, and with no evidence for waning. Similar results were found in sub-group analyses for those ≥50 years of age.”

Key is that protection of natural infection against reinfection wanes and may diminish within a few years. Viral immune evasion accelerates this waning. However, and vey tantalizing is that protection against severe reinfection “remains very strong, with no evidence for waning, irrespective of variant.”