New research published in The Lancet suggests that individuals who have previously been infected with COVID-19 have an 88% lower risk of hospitalization or death than those who have not. The study is the most comprehensive review of data on natural immunity to date, covering data from 65 studies across 19 countries published since January 2021.

The analysis found that the strength and 10-month duration of protection conferred by natural immunity against severe illness is “at least” on par with that provided by two doses of Moderna and Pfizer-BioNtech’s mRNA vaccines. The study’s authors said the data suggests natural immunity in people recently infected with COVID-19 should be recognised by policymakers but warned against using their findings to undermine the importance of vaccination due to the risks associated with the first infection.

“Vaccination is the safest way to acquire immunity, whereas acquiring natural immunity must be weighed against the risks of severe illness and death associated with the initial infection,” lead author Dr Stephen Lim of the University of Washington’s School of Medicine.

Researchers also cautioned that differences between the infectious properties of COVID-19 variants mean protection levels can vary. Infection by pre-Omicron variants, for example, yielded substantially lower natural immunity protection against reinfection by the now dominant Omicron BA.1 variant, with just 36% protection remaining after the 10-month window. Nevertheless, protection against hospitalization and death remained high at 88%.

“The weaker cross-variant immunity with the Omicron variant and its sub-lineages reflects the mutations they have that make them escape built-up immunity more easily than other variants,” report co-author Dr Hasan Nassereldine of the University of Washington’s School of Medicine said. “The limited data we have on natural immunity protection from the Omicron variant and its sub-lineages underscores the importance of continued assessment, particularly since they are estimated to have infected 46% of the global population between November 2021 and June 2022.”

The analysis excluded studies examining “hybrid immunity” (the combination of immune responses from vaccination and natural infection) as well as data relating to Omicron XBB and its sub-lineages. The authors encouraged further research to fill the gaps in the study.