April 16th, 2021 

By Asra Haque 


The phase three clinical trials of the antibody cocktail REGEN-COV, developed by the US-based Regeneron Pharmaceuticals, revealed that a single dose of the drug was effective in protecting individuals exposed to the virus against symptoms. Although the treatment has been given emergency use authorization by the US Food and Drug Administration (FDA) to treat mild-to-moderate coronavirus symptoms, the company is seeking to expand this authorization after receiving encouraging results from the trial.

REGEN-COV (casirivimab with imdevimab) is a cocktail of two monoclonal antibodies (also known as REGN10933 and REGN10987) which was expressly designed to block the infectivity of SARS-CoV-2, the virus responsible for causing the novel coronavirus disease. According to data collected from one trial, the subcutaneous injection provided 72% protection against symptomatic infections in the first week and 93% in the second.

In another trial, it cut down the risk of progressing to symptomatic coronavirus infection by 31% upon administration, and by 76% after the third day. The antibody treatment noticeably decreased the duration of the infection with symptomatic patients on average resolving their symptoms in one week compared to three weeks with a placebo, as well as reducing the amount of the virus present in individuals by more than 90%.

In a new phase three trial, Regeneron provided a single dose of the cocktail or a placebo to 1,505 individuals who did not contract the novel coronavirus disease while living in the same household as another individual who tested positive for the novel coronavirus disease four days prior. The trial saw that REGEN-COV reduced the risk of symptomatic infections by 81% – adverse reactions were observed in 20% of participants who were administered the antibody drug and 29% in those who were administered a placebo.

Over the course of a month, no participant who was administered the drug was hospitalized due to COVID-19 however four who received the placebo did. Of the two deaths among the REGEN-COV group and two among the placebo group, none were due to the drug or the novel coronavirus disease. Regenerov posits that the antibody treatment can help control outbreaks in high-risk settings, and can also complement widespread vaccination strategies.

REGEN-COV is currently produced and administered under emergency use authorization in the US alone, and its phase three trial data has yet to be peer-reviewed. However, the treatment may be an alternative or complement to vaccination programs which have been significantly obstructed due to production issues, export controls, and sluggish and unequal dissemination in countries across the world.