The drug is part of a class of medicines called protease inhibitors and works by inhibiting an enzyme that the virus needs to replicate in human cells, Bourla told the network in an interview. If clinical trials go well and the Food and Drug Administration approves it, the drug could be distributed across the United States by the end of the year, he added.

Pfizer, which developed with German drugmaker BioNTech the first COVID-19 vaccine approved by US health authorities last year, began in March this year an early stage clinical trial that deployed protease inhibitors used for treating viral pathogens such as HIV and hepatitis C, Bourla said.

CNBC quoted health experts as saying the oral drug could be a game changer because people newly infected with the virus could use it outside of hospitals. Researchers hope the new medication will keep the disease from progressing and prevent hospital trips.