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A study by U.S. researchers from Pennsylvania State University, Houston Methodist Hospital, Weill Cornell Medical College, and the CCDC Army Research laboratory in Austin, has investigated what’s the best time-window to collect plasma from COVID-19 convalescent patients. The researchers evaluated the changes with time in the levels of neutralizing antibodies (nAbs) against the virus in samples collected from 175 donors. The short answer: within the first 60 days after symptom onset. During this time, 80% of the individuals with any virus neutralization titer, display levels of neutralization above 160. This is the FDA-recommended value for use in COVID-19 convalescent plasma therapy. However, after this period, and during the next two months, the titers declined rapidly, and at some point only 20% of the individuals still maintain the recommended levels of neutralization.
The researchers also confirmed that neutralization titers are greater if the patients have undergone severe COVID-19 disease, and when the individuals are older. Just the presence of dyspnea (shortness of breath) in the patients, increases the titer of nAbs. Similarly, plasma from individuals in the age interval 20-30, as compared to older than 60-year old patients, are significantly less likely to have the recommended levels of neutralization after 60 days from symptoms start.
The study also confirmed the use of a simple ELISA assay to determine the levels of total antibodies against the receptor binding domain (RBD) of the viral spike protein, as an easy surrogate method to select plasma samples that will neutralize the virus. Virus neutralization assays are more time consuming, require several days, and need laboratory access to biosafety level 3 facilities.
The study is available as preprint in bioRxiv (August 21, 2020): https://doi.org/10.1101/2020.08.21.261909
