One dose of Regeneron's COVID antibody protects for eight months

A single dose of the COVID-19 monoclonal antibody therapy developing Regeneron reduced the risk of contracting the virus by around 82% for up to eight months, according to new trial data.

The results suggest that the REGEN-COV (casirivimab/imdevimab) antibody could play a key role in protecting people who do not mount a sufficiently strong immune response after COVID-19 vaccines, according to the company.

The new findings from the phase 3 trial run by the National Institute of Allergy and Infectious Diseases (NIAID) in uninfected people show that the early protection afforded by the antibody in the first four weeks after dosing is maintained for several months afterwards.

Over the eight-month follow-up period, there were zero hospitalisations for COVID-19 in the REGEN-COV group, compared to six in a matched placebo arm. The rate of COVID-19 vaccination was balanced between the two groups.

It's another first for Regeneron's antibody after it was shown earlier this year to reduce the risk of death, the length of hospital stay and the need for a ventilator among immunocompromised patients in the RECOVERY trial run in the UK.

The new result suggests that REGEN-COV could be used much more broadly than at present.

It has an emergency use authorisation in the US for treating COVID-19 in high-risk individuals – a category that looks hard to defend with new oral antivirals like Merck & Co's molnupiravir and Pfizer's heading to market – as well as for post-exposure prophylaxis if a vulnerable individual is exposed to someone with the virus.

"These data add to the increasing body of evidence supporting use of REGEN-COV to prevent COVID-19 in uninfected individuals," said Regeneron's chief scientific officer George Yancopolous.

"We intend to rapidly share these additional data with regulatory authorities to help those in most need of protection from COVID-19," he added.

If approved, the new use could help REGEN-COV maintain what has developed into blockbuster sales for Regeneron, adding more than $800 million to Regeneron's revenues in the third quarter.

That was down from almost $2.6 billion in the second quarter, but came as a welcome surprise as Regeneron had predicted sales could be almost nil as vaccination levels rose in the key US market.

Prophylaxis for the immunocompromised could help maintain revenues – given there are around 9 million people in that category in the US, according to Centres for Disease Control and Prevention (CDC) estimates.

Regeneron could however face competition in that area from AstraZeneca's ZD7442 (tixagevimab and cilgavimab), another antibody combination which reported positive results earlier this year.