Understanding how antibody levels change over time is critical not only to optimize the use of convalescent plasma but also to understand the efficacy of the vaccine.
Antibody levels in the blood of COVID-19 patients drop rapidly during the weeks after their bodies have cleared the new coronavirus and symptoms have subsided, according to a study.
In the absence of approved and effective treatments for COVID-19, some hospitals have been treating patients with severe symptoms with blood plasma from recovering patients.
If convalescent plasma is ultimately shown to have a clear benefit, the new study published in the journal mBio concluded that it should be collected for a specific period of time after recovery.
However, recovering patients cannot donate blood until at least 14 days after symptoms have disappeared, so that the body has time to clear viral particles.
“We don’t want to transfuse the virus, just transfuse the antibodies,” said Andres Finzi of the University of Montreal in Canada. “But at the same time, our work shows that the ability of plasma to neutralize viral particles is declining during those first few weeks.”
The SARS-CoV-2 spike protein plays a crucial role in helping the virus to grasp and invade host cells. Antibodies produced by the body’s immune system bind to a part of this protein and block the ability of this “key” to interact with the host’s cellular “lock”, preventing the viral particle from infecting a host cell, Finzi said.
Previous studies suggest that antibodies against the SARS-CoV-2 peak protein peak 2 to 3 weeks after the onset of symptoms. Findings from a previous 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 3 and 6 weeks after the onset of symptoms.
In the new longitudinal study, Finzi and his colleagues analyzed blood samples collected at month-long intervals from 31 people recovering from COVID-19.
They measured the levels of immunoglobulins that act against the coronavirus protein S and tested the ability of the antibodies to neutralize the virus. The researchers observed variations in the level of individual patients, but identified a consistent overall signal.
Levels of immunoglobulins G, A and M that target the binding site decreased 6 to 10 weeks after symptoms began, they found. During the same time period, the ability of the antibodies to neutralize the virus similarly decreased, according to the researchers.
Understanding how antibody levels change over time is critical not only to optimize the use of convalescent plasma, but also to understand the efficacy of the vaccine and whether or not previously infected people are at risk of reinfection, they added.
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