Pfizer has started early clinical trials for an oral drug that could possibly fight against COVID-19.

According to reports, the oral drug is a protease inhibitor, a drug that is commonly used to treat HIV and hepatitis C. It works by blocking an enzyme called protease that the virus needs to replicate.

Pfizer’s Chief Scientific Officer Mikael Dolsten said that the oral pill, if approved, could be prescribed at the first sign of infection.

In the meantime, the FDA continues to roll out the COVID-19 vaccine.