Pfizer and German partner BioNTech said that data from a Phase III trial demonstrated high efficacy of a booster dose of their COVID-19 vaccine against the virus, including the Delta variant.
The companies said that the trial, which has not been peer-reviewed, of 10,000 participants aged 16 or older showed 95.6 percent effectiveness against the diseases, during a period when the Delta strain was prevalent. The study also found that the booster shot had a favorable safety profile.
The trial results come a day after the US Food and Drug Administration (US FDA) authorized booster doses of the COVID-19 vaccines from Moderna and Johnson & Johnson, and stated that Americans could choose a different shot from their original vaccination as a booster.
Earlier, Pfizer had said its two-shot vaccine’s efficacy drops over time, citing a study that showed 84 percent effectiveness from a peak of 96 percent four months after a second dose. Some countries had already gone ahead with plans to give booster doses.
The US FDA previously approved boosters of the Pfizer-BioNTech shot at least six months after the first round of shots to enhance protection for people aged 65 and older, those at risk of severe disease and those who are exposed to the virus through their work.
The drugmakers said that the median time between the second dose and the booster shot or the placebo in the study was around 11 months, adding there were only five cases of COVID-19 in the booster group, compared with 109 cases in the group that received the placebo shot.
The median age of the participants was 53 years, with 55.5 percent of participants between 16 and 55 years, and 23.3 percent at 65 years or older.
The companies said they would submit detailed results of the trial for peer-reviewed publication to the US FDA, the European Medicines Agency and other regulatory agencies, as soon as possible.
The US and EU regulators have already authorized a third dose of COVID-19 vaccines from Pfizer-BioNTech and Moderna for patients with compromised immune systems.