Pfizer says antiviral pill cuts risk of severe COVID-19 by 89%

A trial of Pfizer Inc's experimental antiviral pill for COVID-19 was stopped early after the drug was shown to cut by 89% the chances of hospitalization or death for adults at risk of developing severe disease, the company said on Friday.

The results appear to surpass those seen with Merck & Co Inc's pill, molnupiravir, which was shown last month to halve the likelihood of dying or being hospitalized for COVID-19 patients also at high risk of serious illness.

Full trial data is not yet available from either company.

"Just stunning results," Ashish Jha, dean of the Brown University School of Public Health, said in a Twitter post of Pfizer's results. "Implications of effective therapeutics for ending the pandemic are very, very large."

Infectious disease experts stress that preventing COVID-19 through wide use of vaccines remains the best way to control the pandemic, but only 58% of Americans are fully vaccinated and access in many parts of the world is limited.

"Vaccines are going to be the most effective and reliable tool that we have in this pandemic," said Dr. Grace Lee, Professor of Pediatrics, Stanford University School of Medicine. "These oral medications are going to augment our ability to really reduce the risk of severe disease, hospitalization and death, which is huge, but it won't prevent infection."

Shares in Pfizer, which also makes one of the mostly widely used COVID-19 vaccines, were up 7.6% to $47.19 at 1445 GMT, while Merck's were down 8.5% to $82.83. Shares of other vaccine makers also took a hit, with Moderna Inc, Pfizer's German partner BioNTech SE and Novavax all down 10-18%.

Meanwhile, travel stocks rose, with American Airlines, United Airlines, Delta Air Lines, cruise operators Carnival Corp and Norwegian Cruise rising between 4% and 5.9%.

Pfizer said it planned to submit interim trial results for its pill, which is given in combination with an older antiviral called ritonavir, to the U.S. Food and Drug Administration (FDA) as part of the emergency use application it opened in October.

That filing is expected to be submitted before the U.S. Thanksgiving holiday on Nov. 25, Pfizer Chief Executive Albert Bourla said in an interview with CNBC.

The company said it expects to manufacture at least 50 million courses of the oral treatment by the end of 2022.

The combination treatment, which will have the brand name Paxlovid, consists of three pills given twice daily.

The planned analysis of 1,219 patients in Pfizer's study looked at hospitalizations or deaths among people diagnosed with mild to moderate COVID-19 with at least one risk factor for developing severe disease, such as obesity or older age.

It found that 0.8% of those given Pfizer's drug within three days of symptom onset were hospitalized and none had died by 28 days after treatment. That compared with a hospitalization rate of 7% for placebo patients. There were also seven deaths in the placebo group.

Rates were similar for patients treated within five days of symptoms - 1% of the treatment group was hospitalized, compared with 6.7% for the placebo group, which included 10 deaths. Bourla said that works out to being 85% effective.

A panel of outside experts to the FDA is scheduled to meet Nov. 30 to discuss Merck's pill, which was approved by British regulators in a world first on Thursday. Pfizer said it did not know if Paxlovid would be reviewed at the same meeting.

Antivirals need to be given as early as possible, before an infection takes hold in order to be most effective. Merck tested its drug within five days of symptom onset.

"This means that we have time to treat people and really provide a benefit from a public health perspective," Annaliesa Anderson, head of the Pfizer program, told Reuters.

The company did not detail side effects of the treatment, but said adverse events happened in about 20% of both treatment and placebo patients. Ritonavir's possible side effects include nausea and diarrhea.

White House Chief of Staff Ronald Klain said the prospect of an antiviral this effective along with rollout of vaccines for children between the age of 5 and 11 underway could be a turning point week in fight against COVID-19. Klain cautioned that the pill still needed to be reviewed by the FDA.

"These data suggest that our oral antiviral candidate, if approved by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of ten hospitalizations," Bourla said in a statement.

Pfizer said it was currently expecting to produce more than 180,000 packs by the end of 2021 and at least 50 million packs by the end of 2022, of which 21 million would be produced in the first half.

Merck has already made licensing arrangements with some generic drug manufacturers to supply molnupiravir outside of high income countries.

CEO Bourla told Reuters earlier this week that Pfizer was pursuing different options to make its drug available globally. "We are clearly considering, to make sure that we will have enough doses as soon as possible and also equitable access to all, so all options are on the table," he said.

Pfizer's drug, part of a class known as protease inhibitors, is designed to block an enzyme the coronavirus needs to multiply.

Merck's molnupiravir has a different mechanism of action designed to introduce errors into the genetic code of the virus. Merck has already sold millions of courses of the treatment to the United States, Britain and others.

Pfizer is also studying whether its pill could be used by people without risk factors for serious COVID-19 as well as to prevent coronavirus infection in people exposed to the virus.