A new study suggests immunity to coronavirus may drop over several months.
Over 365,000 people across England took finger prick tests from late June to September, as part of Imperial College London’s Real-time Assessment of Community Transmission (REACT) study. Findings were published ahead of peer review on Thursday.
The finger pricks tested for coronavirus antibodies, and results revealed a drop from nearly 6% to 4.4% over a three-month span, which researchers said translates to a 26.5% decline.
If a person tests positive for antibodies, it means they were once infected.
“Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies,” Paul Elliott, study author and professor at Imperial College London, said in a university news release. “It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts.”
The study and university release included suggestions over declining immunity.
“These findings suggest that there may be a decline in the level of immunity in the population in the months following the first wave of the epidemic,” per the university release. Likewise, the study says: “These data suggest the possibility of decreasing population immunity and increasing risk of reinfection as detectable antibodies decline in the population.”
More specifically, the study tested for detectable IgG antibodies. When a virus attacks, the body first produces IgM antibodies, which indicate active or recent infection. IgG antibodies develop later, and often indicate a past infection.
Across three rounds in the REACT study, 17,576 results returned positive, and 30% of people were asymptomatic. The largest reduction in antibody prevalence was among the oldest age group, 75 and above, at 39%, per the university release. The youngest age group saw the least reduction at nearly 15%.
A lead study author stressed the importance of mitigation measures.
“This very large study has shown that the proportion of people with detectable antibodies is falling over time,” said Helen Ward, professor at Imperial College London. “We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes COVID-19, but it is essential that everyone continues to follow guidance to reduce the risk to themselves and others.”