“SARS-CoV-2 infection offered a high level of sustained protection against reinfection, comparable with that offered by vaccines..”
SARS-CoV-2 infection offered a high level of sustained protection against reinfection, comparable with that offered by vaccines, but decreased with the introduction of new main virus variants; dramatically so when Omicron appeared. Protection was lower among the elderly but appeared more pronounced following symptomatic compared to asymptomatic infections. The level of estimated protection against serious disease was somewhat higher than that against infection and possibly longer lasting. Decreases in protection against reinfection, seemed primarily to be driven by viral evolution.
Until 1 July 2021 the estimated protection against reinfection was 83.4% (95%CI: 82.2–84.6%); but lower for the 65+ year-olds (72.2%; 95%CI: 53.2–81.0%). Moderately higher estimates were found for protection against symptomatic disease, 88.3% overall (95%CI: 85.9–90.3%). First-time cases who reported no symptoms were more likely to experience a reinfection (odds ratio: 1.48; 95%CI: 1.35–1.62). By autumn 2021, when infections were almost exclusively caused by the Delta variant, the estimated protection following a recent first infection was 91.3% (95%CI: 89.7–92.7%) compared to 71.4% (95%CI: 66.9–75.3%) after a first infection over a year earlier. With Omicron, a first infection with an earlier variant in the past 3-6 months gave an estimated 51.0% (95%CI: 50.1–52.0%) protection, whereas a first infection longer than 12 months earlier provided only 19.0% (95%CI: 17.2–20.5%) protection. Protection by an earlier variant-infection against hospitalisation due to a new infection was estimated at: 86.6% (95%CI: 46.3–96.7%) for Alpha, 97.2% (95%CI: 89.0–99.3%) for Delta, and 69.8% (95%CI: 51.5–81.2%) for the Omicron variant.
Image by Armed Forces Institute of Pathology/National Museum of Health and Medicine, distributed via the Associated Press, Public domain, via Wikimedia Commons