Pfizer said Tuesday it had started an early clinical trial of an experimental oral antiviral drug for Covid-19.

The New York-based company announced that the Phase 1 study of the drug PF-07321332 will be conducted in the United States. The drug belongs to a class of drugs called protease inhibitors, and it works by blocking an enzyme that the virus needs to replicate in human cells.

Protease inhibitors are used to treat other viral pathogens such as HIV and hepatitis C.

“Fighting the COVID-19 pandemic requires both preventive vaccination and targeted treatment of those who become infected with the virus,” Pfizer’s chief scientist Mikael Dolsten said in a press release. “Given the way SARS-CoV-2 is mutating and the ongoing global impact of COVID-19, it is likely that access to therapeutic options will be critical both now and after the pandemic.”

The study comes as Pfizer is also working on an intravenously administered protease inhibitor known as PF-07304814. This drug is currently in a Phase 1b clinical trial in patients hospitalized with Covid-19.

A person walks past the Pfizer building in New York City on March 2, 2021.

Carlo Allegri | Reuters

Pfizer already has an approved vaccine in the US with German drug maker BioNTech, but health experts say the world will need a slew of drugs and vaccines to end the pandemic that is infecting more than 29.8 million Americans and is coming soon Has killed at least 542,991 people over a year, according to the Johns Hopkins University.

Preclinical studies have shown that the oral drug, the first orally ingested protease inhibitor for Covid-19 to be studied in clinical trials, has “strong” antiviral activity against the virus.

Because the drug is taken orally, it can be used outside of hospitals for people newly infected with the virus. The researchers hope the drugs will prevent the disease from getting worse and keep people out of the hospital.

Pfizer said it will provide more details on the drug at the Spring American Chemical Society meeting on April 6.