Pfizer Inc has said the final analysis of its antiviral COVID-19 pill showed close to 90 percent efficacy in preventing hospitalisations and deaths in high-risk patients with recent lab data suggesting the drug retains its effectiveness against the fast-spreading Omicron variant of the coronavirus.

The US drugmaker’s remarks came on Tuesday after it said last month the oral medicine was about 89 percent effective in preventing hospitalisations or deaths when compared with placebo based on interim results in about 1,200 people.

The data disclosed on Tuesday includes an additional 1,000 people.

Nobody in the trial who received the Pfizer treatment died, compared with 12 deaths among placebo recipients.

The Pfizer pills are taken with the older antiviral ritonavir every 12 hours for five days beginning shortly after the onset of symptoms.

If authorised, the treatment will be sold as Paxlovid.

Pfizer also released early data from a second clinical trial showing that the treatment reduced hospitalisations by approximately 70 percent in about 600 standard-risk adults.

“It’s a stunning outcome,” Pfizer Chief Scientific Officer Mikael Dolsten said in an interview.

“We’re talking about a staggering number of lives saved and hospitalisations prevented. If you deploy this quickly after infection, we are likely to reduce transmission dramatically,” Dolsten added.

There are currently no oral antiviral treatments for COVID-9 authorised in the United States.

Rival Merck & Co has asked for emergency use authorisation of its antiviral pill molnupiravir. But that drug reduced hospitalisations and deaths in its clinical trial of high-risk patients by only about 30 percent.

Pfizer shares fell 0.8 percent to $54.75 in trading before the bell, while Merck shares were flat at $72.69.

Dolsten said recent laboratory testing showed that the activity against the protease of the Omicron variant is as “good as basically any SARS-COV-2 variant of concern”.