Abstract

The emergence of the novel human coronavirus SARS-CoV-2 in Wuhan, China has caused
a pandemic of respiratory disease (COVID-19). Effective clinical intervention strategies for
COVID-19 are urgently needed. Although several clinical trials have evaluated the use of
convalescent plasma containing virus-neutralizing antibodies, the effectiveness has not
been proven. We show that hamsters treated with a high dose of human convalescent
plasma or a monoclonal antibody were protected against weight loss showing reduced

pneumonia and pulmonary virus replication compared to control animals. However, a ten-
fold lower dose of convalescent plasma showed no protective effect. Thus, variable and

relatively low levels of virus neutralizing antibodies in convalescent plasma may limit their
use for effective antiviral therapy, favouring concentrated, purified (monoclonal) antibodies.