COVID-19 Antibody Study

The relationship between the presence of antibodies to COVID-19 and the risk of subsequent reinfection remains unclear, and doubts have been raised about whether infection with COVID-19 renders any immunity to the individual against reinfection or not.

Researchers have found in a new study that people who made antibodies to the coronavirus were much less likely to test positive again for up to six months and maybe longer. Very few healthcare workers in the United Kingdom who recovered from COVID-19 and had immunoglobulin G (IgG) antibodies against the virus were reinfected over the next 6 months.

The results of the study have been published on Dec 23 in the New England Journal of Medicine.

The researchers conducted a prospective, longitudinal cohort study in which levels of IgG antibodies against the coronavirus's spike protein and nucleocapsid were measured in symptomatic and asymptomatic healthcare workers at Oxford University Hospitals undergoing COVID-19 testing between Mar 27 and Nov 30.

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 the 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 future studies in children, older people, and those with underlying medical conditions such as immunosuppression.