Pfizer’s antiviral pill is highly effective at preventing people who catch COVID-19 from becoming seriously ill, the company said today in a press release. A clinical trial showed that the pill, which has the brand name Paxlovid, cut the risk of hospitalization and death by 89 per cent for adults at high risk of developing the severe disease when it was given within three days of symptoms appearing.

The company said it plans to submit its data to the Food and Drug Administration (FDA) for emergency use authorization “as soon as possible.”

This is the second effective anti-COVID-19 pill. The first, developed by pharmaceutical company Merck, cut the risk of hospitalization and death by about half. The United Kingdom’s health agency authorized the Merck pill on Thursday, and the FDA’s advisory committee is scheduled to discuss it on November 30th.

Pfizer tested its drug in a study that included 1,219 adults who tested positive for COVID-19, had mild or moderate symptoms, and who had at least one underlying medical condition that would put them at risk for a severe case of the disease (like diabetes or a lung condition). Participants were randomly assigned to either take a course of placebo pills or the active drug. Three people in the active drug group were hospitalized and none died. In the placebo group, 27 people were hospitalized and seven died. The data was announced in a press release and has not been published in a scientific journal.

The Pfizer treatment works by stopping the coronavirus from making copies of itself inside cells. It includes 30 pills taken over five days. Merck’s, which works in a similar way, requires 40 pills taken over five days. Both are cheaper than treatments like monoclonal antibodies, which also can keep people from becoming seriously ill. They’re also logistically easier to use — pills can be taken at home, while antibody treatments are given through an infusion at a health centre.

The challenge with antiviral treatments like the Pfizer pill is ensuring that people are able to access them in the short window when they’re most effective. If people aren’t able to get a COVID-19 test result or make it to a doctor within the first few days after they start feeling sick, they likely won’t be able to get the same benefits from the drug.

Medications are taken after someone gets sick also aren’t a replacement for vaccines, which can prevent people from getting sick in the first place. But antiviral pills are an important tool to fight COVID-19. “I think getting an oral pill that can inhibit viral replication — that can inhibit this virus — is going to be a real game-changer,” former FDA commissioner Scott Gottlieb told CNN in October.

TodayNG