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Immunity acquired after being sick with COVID offers high levels of protection against severe disease development for up to 10 months, according to a systematic review and meta-analysis published Thursday in the journal The Lancet.
According to the data analyzed, protection against severe disease remains high at 88 percent or higher up to 40 weeks after being infected with SARS-CoV-2 variants such as alpha and deltaas well as with the omicron subvariant BA.1.
The research also suggests that the level and duration of protection against reinfection, symptomatic disease, and severe disease are at least equal to that provided by two doses of the Moderna, Pfizer-BioNtech mRNA vaccines for the strains before mentioned. The study did not include data on infection of omicron XBB and its sublineages.
“Vaccination is the safest way to acquire immunity, while the acquisition of natural immunity must be weighed against the risks of severe illness and death associated with the initial infection,” said lead author Dr. Stephen Lim of the Metrics Institute. and Washington University School of Medicine Health Evaluation (IHME) in a news release.
Since January 2021, several studies and reviews have reported on the efficacy of past COVID-19 infections in reducing the risk of reinfection and how immunity wanes over time but none have comprehensively assessed how long protection lasts after natural infection and what so durable it is against different variants, the statement said.
In order to dispel these doubts, IHME researchers conducted a review and meta-analysis of 65 previous studies in 19 countries that compared the reduction in risk of COVID-19 between unvaccinated people against SARS-CoV-2 reinfection with unvaccinated people without a previous infection. What did they find?
Natural immunity against reinfection of COVID decreases over time
Analysis of data from 21 studies that reported on time elapsed since infection with a pre-omicron variant estimated that the protection against reinfection with the same variants was 85 percent per monthand dropped to about 79 percent at 10 months. While the protection acquired after infection by the pre-omicron variant against the BA.1 subvariant was 74 percent at one month and decreased more rapidly, to 36 percent at around 10 months.
However, analysis of five studies that reported severe illness leading to hospitalization and death found that protection remained universally high over 10 months: 90 percent for alpha and delta variants, and 88 percent for BA. 1.
Six studies evaluating protection against omicron sublineages, specifically BA.2 and BA.4/BA.5, suggested a significantly reduced protection when the previous infection was caused by a pre-omicron variant. However, when the previous infection was with omicron, the protection remained at a higher level.
Despite the revealing results, the researchers caution that data on the BA.1 subvariant, its sublineages, and subsequent data 10 months after initial infection were limited. They also clarify that some of the information, such as prior infection status and hospital admissions, was measured differently or was incomplete, and could bias the estimate of protection.
