Post exposure prophylaxis means taking medicine after exposure to the SARS-COV virus in order to prevent infection. The approval was based on the results of a large phase 3 study which showed that taking Casirivimab/Imdevimab within 96 hours of exposure to a person living in the same house infected with SARS COV-2 virus significantly reduced the risk of symptomatic infection by 81.4 %. Only 11 of 753 people exposed to the virus (1.5%) developed symptomatic infection compared to 59 of 752 (7.8%) participants who were given placebo. Among those who got infected despite taking antibody cocktail, symptoms resolved faster and the duration of high viral load was lower (NEJM 2021)**.
Antibody cocktail is indicated for restricted use in emergency situation for post-exposure prophylaxis of COVID-19 in adults (≥ 18 years) who are at high risk for progression to severe COVID-19, including hospitalization or death, and:
O'Brien MP, Forleo-Neto E, Musser BJ, et al. Subcutaneous REGEN-COV Antibody Combination for Covid-19 Prevention.N Engl J Med. 2021 Aug 4.