RAPIDLY falling levels of antibodies have been demonstrated in the plasma of patients recovering from coronavirus disease (COVID-19). The recent study findings have implications for the use of convalescent plasma therapy in the treatment of severe cases of COVID-19.
Antibodies that develop against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) target the spike protein of the virus to impede invasion of host cells. Previous studies have suggested that levels of these antibodies peak 2 or 3 weeks after symptom onset, while another study suggested that the efficacy of convalescent plasma therapy fell significantly 3–6 weeks after symptom onset.
A longitudinal study, led by Dr Andrés Finzi, University of Montreal, Montreal, Canada, collected blood samples from 31 patients recovering from COVID-19, with sampling and analysis at 1-month intervals. The study tested both levels of the antibodies and their ability to neutralise the SARS-CoV-2 virus. IgG, IgA, and IgM all fell 6–10 weeks after symptom onset, with similar falls in activity against the virus. Dr Finzi summarised: “Our work shows that the capacity of the plasma to neutralise viral particles is going down during those first weeks.”
Although there was variation between individual patients’ antibody levels, the researchers found the overall trend of rapid reduction to be consistent across the group. Understanding patterns of antibody levels is important for the utility of convalescent plasma as a therapy option because plasma collection must be delayed to 14 days post-symptom onset to allow time for viral particles to be cleared from the infected donor. These results support a narrow window for collecting convalescent plasma. Convalescent plasma therapy has not yet been shown to be effective in randomised trials; however, smaller retrospective studies suggest that it may reduce length of hospitalisation and severity of illness.
Dr Finzi and the researchers are continuing their studies on antibody levels and activity in COVID-19, as insights will help not only in convalescent plasma therapy, but in determining how long potential post-infection immunity may persist, assisting vaccine planning.