The outside of the Pfizer world headquarters building in New York City is seen in this photo taken on May 5, 2014. Photo: Spencer Platt/Getty Images

Pfizer announced the beginning of a phase 1 clinical trial using a protease inhibitor pill as a treatment for the virus on Tuesday. News of the trial comes months after Pfizer's COVID-19 vaccine, made in collaboration with the German firm BioNTech, was approved for use and began to be administered in the U.S. and several other countries. The pill, currently dubbed PF-07321332, could offer an additional weapon against the virus as fast-moving mutations threaten to weaken the effectiveness of vaccines.

"Tackling the COVID-19 pandemic requires both prevention via vaccine and targeted treatment for those who contract the virus," Pfizer's Chief Scientific Officer Mikael Dolsten said in a statement obtained by Newsweek. "Given the way that SARS-CoV-2 is mutating and the continued global impact of COVID-19, it appears likely that it will be critical to have access to therapeutic options both now and beyond the pandemic."

"We have designed PF-07321332 as a potential oral therapy that could be prescribed at the first sign of infection, without requiring that patients are hospitalized or in critical care," added Dolsten.

The drug has shown activity against the virus that causes COVID-19 in test tube experiments, as well as activity against other types of coronaviruses, with the company saying that the results raise the possibility of "potential use to address future coronavirus threats."

Dolsten touted both the oral medication and the company's previously-developed experimental protease inhibitor treatment designed to be administered to hospitalized COVID-19 patients intravenously, which is currently undergoing phase 1b trials. Dolsten said that that two different approaches offer "the potential to create an end to end treatment paradigm that complements vaccination in cases where disease still occurs."

While none of the vaccines offer total protection against contracting the virus, they have been shown to significantly reduce infections and to be extremely effective in preventing hospitalizations and death. Treatment options could help mitigate concerns posed by the fact that some of the mutations currently making their way around the world have shown a limited amount of resistance to the vaccines, although both Pfizer and Moderna are developing booster shots or new versions of vaccines to combat emerging variants.

As of Tuesday, over 64.6 million people in the U.S. had received at least one dose of the Pfizer-BioNTech vaccine, according to the Centers for Disease Control and Prevention. Moderna's vaccine was not far behind, with around 60.9 million doses administered, while the single-dose Johnson & Johnson vaccine had gone into the arms of just under 2.5 million people.

Protease inhibitors, which block virus reproduction by binding to proteins called protease, were a class of drugs that revolutionized HIV treatment in the mid-1990s. They are key components in the multi-drug "cocktail" therapies that changed HIV from an infection that almost invariably led to AIDS and death to a condition that can typically be survived if treatments are available and used regularly. The drugs are also used against Hepatitis C infections, while researchers have investigated their use as treatments for certain types of cancer and parasitic infections.