A booster dose of Pfizer-BioNTech’s coronavirus vaccine is 95.6% effective in preventing symptomatic infections of the disease, the two companies announced on Thursday.

The vaccine makers released results from phase three of trials to evaluate the efficacy and safety of a third dose of the vaccine. The trial was conducted on more than 10,000 people above 16 years of age.

While half of the participants got a booster dose of the vaccine, the other half received a placebo. After two-and-a-half months, five people in the first group were infected with Covid-19, while 109 people were infected from the second group.

Pfizer and BioNTech said that they were planning to submit the trial results for peer-reviewed publication.

“These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease,” a press release quoted Pfizer Chief Executive Officer Albert Bourla as saying. “In addition to our efforts to increase global access and uptake among the unvaccinated, we believe boosters have a critical role to play in addressing the ongoing public health threat of this pandemic.”

BioNTech Chief Executive Officer Ugur Sahin said that the data adds to “the body of evidence suggesting that a booster dose of our vaccine can help protect a broad population of people from this virus and its variants”.

The two companies noted that the study was conducted at a time when the Delta variant of Covid-19 was the prevalent strain.

Pfizer-BioNTech’s vaccine

The vaccine, developed by United States-based pharmaceutical company Pfizer and German biotechnology company BioNTech, was authorised by US regulators in late December for people aged 16 and older. After that, more than 65 countries have used it to vaccinate millions of adults against the infection, according to AFP.

On September 22, the United States gave authorisation for the use of booster shots of the vaccine for high-risk adults and those aged 65 and above.

The third shot will be administered at least six months after the second dose, the Food and Drug Administration said.

On Wednesday, the US FDA also approved a booster dose for eligible individuals who have completed primacy vaccination with a different coronavirus vaccine.