People who had COVID-19 had an 84% lower risk of becoming reinfected and a 93% lower risk of symptomatic infection during 7 months of follow-up, according to findings from a large, multicenter study published late last week in The Lancet.
The prospective cohort SARS-CoV-2 Immunity and Reinfection Evaluation (SIREN) study, by Public Health England Colindale researchers, involved 25,661 workers at public hospitals throughout England who were tested for SARS-CoV-2 every 2 to 4 weeks and antibodies at enrollment and every 4 weeks. Volunteers also completed questionnaires on symptoms and exposures every 2 weeks.
Of the 25,661 participants, 32.3% were assigned to the baseline positive (possibly or probably previously infected) group, and 67.7% were assigned to the negative group. Of the 8,278 positive participants, 91.2% had SARS-CoV-2 antibodies at study enrollment, while 7.0% were negative for antibodies but had a previously positive antibody and/or coronavirus test, and 1.8% had tested positive for COVID-19 but didn’t have linked antibody data.
Natural immunity vs vaccine protection
In a commentary in the same journal, Florian Krammer, PhD, of the Icahn School of Medicine at Mount Sinai in New York City, said that although natural infection tends to induce lower and more variable antibody concentrations than COVID-19 vaccines, “the findings of the authors suggest that infection and the development of an antibody response provides protection similar to or even better than currently used SARS-CoV-2 vaccines.
He added, “The SIREN study adds to a growing number of studies, which demonstrate that infection does protect against reinfection, and probably in an antibody-dependent manner.”
Krammer pointed out that the researchers didn’t link quantitative antibody measurements to protection against infection afforded by natural infection versus vaccines, a topic that should be a priority for future studies.
“Establishment of antibody titres as a correlate of protection and defining a protective titre would be extremely important for public health considerations and for patient management,” he wrote. “A correlate of protection and a protective threshold would also allow for the development of additional SARS-CoV-2 vaccines based on small immunogenicity-based phase 3 trials rather than large and costly field efficacy trials, which are becoming exceedingly difficult to perform.”