Previous studies suggest that antibodies against the SARS-CoV-2 spike protein peak two or three weeks after the onset of symptoms. Findings from an earlier cross-sectional study by Finzi's group, involving more than 100 patients, suggested that the ability of plasma to neutralize the virus decreased significantly between three and six weeks after symptom onset.
In the new longitudinal study, Finzi and his colleagues analyzed blood samples collected at one-month intervals from 31 individuals recovering from COVID-19. They measured levels of immunoglobulins that act against the coronavirus S protein and tested the ability of the antibodies to neutralize the virus.
The researchers observed variation on the level of individual patients but identified a consistent overall signal: The levels of Immunoglobulins G, A, and M that target the binding site decreased between six and 10 weeks after symptoms began. During the same time period, the ability of the antibodies to neutralize the virus similarly fell.
Finzi's group has continued to study blood samples from the patients. Understanding how the levels of antibodies change over time, he said, is critical not only for optimizing the use of convalescent plasma but also for understanding vaccine efficacy and whether or not previously infected people are at risk of re-infection. "How long do antibodies protect you?" Finzi asked.
