Population
Adult COVID-19 outpatients (5 studies, n= 2,620).
Intervention
Intravenous COVID-19 convalescent plasma (CCP) transfusion (n= 1,305).
Comparison
Non-convalescent plasma or normal saline (n= 1,315).
Outcome
The virus neutralizing antibody dilutional titre levels ranged from 8 to 14,580 in diverse assays. 160 (12.2%) of 1,315 control patients were hospitalized, versus 111 (8.5%) of 1,305 COVID-19 convalescent plasma treated patients, yielding a 3.7% (95% CI: 1.3% - 6.0%) absolute risk reduction and 30.1% relative risk reduction for all-cause hospitalization. The hospitalization reduction was greatest in those with both early transfusion and high titre with a 7.6% absolute risk reduction (95% CI: 4.0% - 11.1%) accompanied by at 51.4% relative risk reduction. No significant reduction in hospitalization was seen with treatment > 5 days after symptom onset or in those receiving COVID-19 convalescent plasma with antibody titres below the median titre.