REGEN-COV works as COVID post-exposure prophylaxis, study says

Using the monoclonal antibody cocktail REGEN-COV reduced the risk for symptomatic COVID-19 infection 81% in those exposed to a COVID patient, according to a New England Journal of Medicine study yesterday.

The findings were used in the US Food and Drug Administration's recent decision to expand the drug's emergency-use authorization; now, it can be used as post-exposure prophylaxis in high-risk populations, not just a treatment during infection.

All COVID-19 cases reduced by 66%

The study included 1,505 people ages 12 and up who never had COVID-19 and who had a household member test positive within 96 hours (median age, 42.9 years). Half received via subcutaneous (under-the-skin) injection 1,200 milligrams of REGEN-COV, which is a combination of the monoclonal antibodies casirivimab and imdevimab, and half received a placebo by Jan 28, 2021.

By day 28, COVID-19 infection developed in 1.5% of the intervention arm versus 7.8% of the placebo arm (relative risk reduction [RRR], 81.4%). When including asymptomatic infections, RRR for REGEN-COV treatment was 66.4%.

Adverse events such as injection-site pain and headache occurred in 1 in 5 REGEN-COV recipients (20.2%) and 29.0% of placebo recipients, although 16.0% and 16.5% were non–COVID-related, respectively. None were of special interest, including the serious adverse events that occurred in 0.8% of the REGEN-COV group and 1.1% of the placebo group. Four deaths occurred, two in each group, but none were related to the study.

"This trial showed that, throughout the 28-day observation period, the achieved concentrations of a single subcutaneous dose of REGEN-COV prevented symptomatic infection; thus, REGEN-COV has potential use as long-term prophylaxis in persons at risk for SARS-CoV-2 infection," the researchers write, noting that many of the study participants had a high-risk COVID-19 factor such as old age (with or without other conditions such as cardiovascular disease), high body mass index, or diabetes.

Infections shorter, milder

For patients who became infected with COVID-19, those who were injected with REGEN-COV were more likely to have a milder disease course. For instance, illness was shorter (1.2 vs 3.2 weeks), high viral loads less likely (1.5% vs 11.3%), and duration of high viral load shorter (0.4 vs 1.3 weeks).

Also, none of the COVID-19 patients who received REGEN-COV needed hospitalization; whereas, 4 (0.05%) of those who received a placebo did.

The researchers note that, during the first week post-treatment, 1.2% of the intervention group versus 4.3% of the placebo group had symptomatic COVID-19 infection (RRR, 71.9%), while weeks 2 to 4 saw 0.3% and 3.6% of the total intervention and placebo groups, respectively, develop infection (RRR, 92.6%).

When stratified by age, the data suggested that REGEN-COV had 100% RRR for children younger than 18 years, 78.1% RRR for people age 50 and above, and 89.7% for those 65 and older. These subgroups, however, were relatively small (eg, 46 adolescents who received REGEN-COV vs 43 who did not).

"These data provide support for the potential use of REGEN-COV to prevent SARS-CoV-2 infection and symptomatic disease in persons in whom immediate protection is warranted," the researchers conclude. "The use of REGEN-COV in such persons could decrease further spread and transmissibility of SARS-CoV-2 infection."

They add, "Our trial also showed that subcutaneous administration of REGEN-COV was efficacious and had an acceptable safety profile; thus, it may provide substantial benefits because the health care resources necessary for an intravenous infusion may be avoided."

Newsletter Sign-up

Get CIDRAP news and other free newsletters.

Sign up now»


Unrestricted financial support provided by

Bentson Foundation Unorthodox Philanthropy logo and text 'Leading Underwriter'3M logoGilead 
Grant support for ASP provided by


  Become an underwriter»