Pfizer says its booster shot has 95.6% efficacy against COVID-19 amid the Delta variant

• Pfizer said fully vaccinated people who got an extra dose of its vaccine were at much lower risk of COVID-19.
• The findings come from Pfizer's late-stage trial of more than 10,000 people aged 16 and older.
• The study hasn't yet been published or formally scrutinized by other experts.

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Fully vaccinated people who received a booster dose of Pfizer's shot in a large trial were at much lower risk of catching COVID-19, the company said Thursday.

This group was at a 95.6% lower risk of catching COVID-19 than fully vaccinated people who received a dummy vaccine, called a placebo, instead of the booster, the company said.

It reported no safety concerns from the trial.

"These are the first efficacy results from any randomized, controlled COVID-19 vaccine booster trial," Pfizer said in the press release, adding that it planned to submit the data to health authorities.

The results were from a late stage trial of more than 10,000 people aged 16 or older. 

Pfizer Chairman and CEO Albert Bourla said in the statement: "These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease."

Pfizer's vaccine is already authorized as a booster in the US and UK for people at high risk of COVID-19.

To get the 95.6% figure, the researchers compared how many people in the booster group got COVID-19 with the number of people in the placebo group that caught the virus.

There were five cases of COVID-19 in the "boosted group" and 109 cases in the "non-boosted group" during the study period, Pfizer said.

Pfizer said that the booster provided the same amount of protection across all age groups. About half of people in the trial were aged 16 to 55, and just under a quarter were 65 and older, it said.

The researchers looked at whether people got COVID-19 with symptoms from seven days after the booster. They followed up after two and a half months on average, so we still don't know how long booster protection from Pfizer's shot lasts.

The results of the trial haven't been published or scrutinized by other experts.