Earlier COVID-19 infection appears to protect for at least 6 months: NEJM

The study screened more than 12,500 health workers at Oxford University Hospitals in the United Kingdom. Out of 1,265 who had coronavirus antibodies at the outset, only two had positive results on tests to detect active infection in the following six months and neither developed symptoms.

That contrasts with the 11,364 workers who initially did not have antibodies; 223 of them tested positive for infection in the roughly six months that followed.

The authors noted that the presence of anti-spike antibodies was linked with a much lower risk of SARS-CoV-2 infection over follow-up and that only two COVID-19 reinfections occurred in antibody-positive workers, both of them asymptomatic, "which suggests that previous infection resulting in antibodies to SARS-CoV-2 is associated with protection from reinfection for most people for at least 6 months," they said.

The study concluded that presence of anti-spike or anti-nucleocapsid IgG antibodies was associated with a substantially reduced risk of SARS-CoV-2 reinfection in the ensuing 6 months.

However it could not be concluded whether past positive antibody results or current levels determine immunity or whether the protection is conferred through the antibodies measured or through T-cell protection, which was not evaluated. The authors recommended for future studies in children, older people, and those with underlying medical conditions such as immunosuppression.