Regeneron said Monday that a single dose of its antibody cocktail reduces the risk of symptomatic COVID-19 infection by 81.6% up to eight months later.

The results from the Phase 3 clinical trial show that the treatment maintains the 81.4% effectiveness that was reported one month after being administered.

The New York-based drugmaker says the antibody cocktail, called REGEN-COV, could provide long-lasting immunity to people who do not respond to COVID-19 vaccines, including people who are immunocompromised.

REGEN-COV, which combines the monoclonal antibodies casirivimab with imdevimab, is administered through four subcutaneous injection. It uses human antibodies without any artificial mutations or sequences. 

The clinical trial was conducted jointly with the National Institute of Allergy and Infectious Diseases.

"In this trial, a single dose of REGEN-COV provided long-term protection against COVID-19, including times of particularly high risk from household exposure, and in the longer-term during ongoing broader exposure," Dr. George Yancopoulos, president and chief scientific officer at Regeneron, said in a news release. "These data add to the increasing body of evidence supporting use of REGEN-COV to prevent COVID-19 in uninfected individuals, which may be especially useful for the many immunocompromised people who do not respond adequately to vaccines and remain 'prisoners of the pandemic.'”

The clinical trial enrolled 1,683 people. None of those who were given REGEN-COV were hospitalized, compared to six in the placebo group. 

The Food and Drug Administration has granted emergency use authorization for REGEN-COV to be given to people at risk for severe COVID-19, including infected individuals who had not been hospitalized and people who have been exposed to someone with the virus, such as a household member, but who have not tested positive themselves. The trial only monitored people who had not been infected and did not have antibodies for COVID-19.

Regeneron said it will share the new data with regulators “to help those in most need of protection from COVID-19.” It also said it is partnering with Swiss pharmaceutical company Roche to increase global supply for the antibody cocktail, with Roche primarily responsible for developing and distributing it outside the U.S.

Regeneron CEO Len Schleifer, however, told CNBC on Monday that he doesn’t think his company can produce enough antibodies at an affordable price to use them as widely as vaccines. 

“If you’re in the military or you’re a teacher or you’re on the frontline and you legitimately have this fear, maybe this can be offered as an alternative,” he said. “It’s something we have to discuss. But the data — put the politics aside — the data say that antibodies can protect you from getting COVID-19.”

Schleifer added that immunocompromised people could eventually receive the antibody cocktail every five or six months and “be protected just as though they were vaccinated.”