These drugs are designed to be taken by people who test positive for COVID, early in their infection. Current antivirals are administered by intravenous drip, whereas the pills promise a much easier and more scalable at-home approach to treatment. They are still not substitutes for vaccination, however.

Merck announced just over a month ago that its antiviral, molnupiravir—which it developed alongside Ridgeback Biotherapeutics—halved the risk of at-risk patients requiring hospitalization, or dying. Since then, the company has taken the unprecedented step of allowing the production of generic versions of molnupiravir in low- and middle-income countries, so as to ensure sufficient production levels and equitable distribution. The U.K. drug regulator granted the pill’s first national authorization this week.

However, Pfizer said Friday that its antiviral—Paxlovid—was even more effective at reducing hospitalization and death, with an 89% efficacy rate among patients who were “at high risk of progressing to severe illness.” The results were sufficiently positive to see Pfizer close enrollment in its trial, although, as with Merck, the company has yet to publish its full trial data.

“Today’s news is a real game changer in the global efforts to halt the devastation of this pandemic,” said Pfizer chief executive Albert Bourla. “These data suggest that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of 10 hospitalizations.”

Pfizer’s share price shot up by 13% on the announcement, while Merck was at one point down more than 10%.

In the trial, just 0.8% of patients who received the drug within three days of developing symptoms were in hospital four weeks after their treatment; the rate was 7% for trial participants who got the placebo. For those who took it within five days of symptom onset, the hospitalization rate at 28 days was 1%, compared with 6.7% for those who did not take Paxlovid.

Bourla promised to ensure “equitable and broad access to people everywhere.” However, Pfizer’s announcement made no mention of following Merck’s lead in allowing generic versions. Instead, the company said it would charge poorer countries less than it charges rich countries, and explore “potential contract manufacturing options to help ensure access across low- and middle-income countries, pending regulatory authorization.”

Pfizer said multiple countries had already signed up to buy Paxlovid, adding the drug has “potential as a therapeutic for multiple types of coronavirus infections.”