Pfizer, Inc. and BioNTech SE announced Thursday that topline results from a Phase 3 trial found that a 30-microgram booster dose of the companies' vaccine showed a relative vaccine efficacy of 95.6% in individuals who had previously received the Pfizer/BioNTech primary two-dose series, when compared to those who did not receive a booster.
The trial included more than 10,000 people who were 16 years old or older and Pfizer said in a news release that the booster dose administered to the participants restored vaccine protection against COVID-19 "to the high levels achieved after the second dose."
The individuals were randomized to receive either a 30-microgram booster dose – the same dosage as in the primary series – or a placebo.
The midpoint between the second Pfizer/BioNTech vaccine dose and administration of either the booster dose or a placebo was around 11 months.
Symptomatic COVID-19 occurrence was measured from at least seven days after booster or placebo, with a median follow-up time of approximately two-and-a-half months.
There were five cases of COVID-19 recorded in the booster group and 109 in the non-boosted group.
The median age of participants was 53 years old and subgroup analyses showed that the efficacy of the booster was consistent regardless of age and other factors like sex, race, ethnicity and comorbid conditions.
The adverse event profile, Pfizer noted, was "generally consistent with other clinical safety data for the vaccine, with no safety concerns identified."
The results, the company said, are the first from any randomized, controlled COVID-19 vaccine booster trial.
"These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease," Pfizer CEO Albert Bourla said in a statement.
Pfizer and BioNTech plan to submit the results from the trial for peer-reviewed publication, as well as share the data with the U.S. Food and Drug Administration (FDA), European Medicines Agency and other regulatory agencies.
In September, a Pfizer/BioNTech booster dose was authorized for emergency use by the FDA for individuals 65 years of age and older, individuals 18 through 64 years of age at high risk of severe COVID-19, and individuals 18 through 64 years of age with frequent institutional or occupational exposure to the virus.
On Wednesday, a booster dose was also authorized for emergency use by the FDA for eligible individuals who have completed a primary vaccination with a different authorized COVID-19 vaccine.