Duration of anti-SARS-CoV-2 antibodies in plasma is currently unknown; while the overall antibody responses for other betacoronaviruses typically declines after six to twelve months, SARS-specific neutralizing antibodies usually persist for two years.
So in the vast majority of countries, a suitable donor could donate 600 ml of plasma (equivalent to three therapeutic doses under most current trials) every 14 days for a minimum of six months. Up to seven plasma donations have been proven not to decrease antibody titers in convalescent donors.
In contrast to SARS and MERS patients, most COVID-19 patients exhibit few or no symptoms and do not require hospitalization; this could suggest that the majority of convalescent donors are best sought in the general population although specific studies on antibody titers in mildly symptomatic patients suggest low titers.
Among patients with severe or life-threatening COVID-19, convalescent plasma therapy added to standard treatment, compared with standard treatment alone, did not result in a statistically significant improvement in time to clinical improvement within 28 days. Interpretation is limited by early termination of the trial, which may have been underpowered to detect a clinically important difference.