The booster programmes underway in many countries to combat the COVID-19 pandemic have received their own boost with results from the first phase 3 randomised, controlled clinical trial.
Top-line results show that a booster dose of Pfizer-BioNTech’s vaccine, Comirnaty, administered to 10,000 people over the age of 16 who completed the original two-dose regimen restored vaccine protection against COVID-19 to the high levels achieved after the second dose.
The third dose – on average given 11 months after the second dose – caused a relative vaccine efficacy of 95.6% when compared to those who did not receive a booster.
Recipients of the booster shot were followed up after 2.5 months on average, during which time there were five cases of COVID-19 in the booster group and 109 cases in the non-boosted group. The trial also took place at a time when the much more transmissible Delta variant of SARS-CoV-2 was the dominant strain circulating.
“These results provide further evidence of the benefits of boosters,” said Pfizer CEO and chairman, Albert Bourla. “We believe boosters have a critical role to play in addressing the ongoing public health threat of this pandemic.”
The results from the trial will be shared with the Food and Drug Administration, European Medicines Agency and other regulatory agencies worldwide, said Bourla.
Dr Ugur Sahin, CEO and co-founder of BioNTech, emphasised that the booster dose “can help protect a broad population of people from this virus and its variants”. The median age of trial participants was 53 years and multiple subgroup analyses showed that the jab was effective across age, sex, race, ethnicity and comorbid conditions.
The trial results have been welcomed by the scientific and medical community. For Andy Hill, senior visiting research fellow in pharmacology at the University of Liverpool, the trial was “very important” as it offered “much stronger” evidence.
Hill said: “It is randomised and measures effects on new infections. This is a big step forward from previous studies of other vaccines which only measured effects on antibody levels. This new trial is much more reliable.”
However, some experts are more cautious. Amesh Adalja from the Johns Hopkins Center for Health Security asked several questions about breakthrough infections, or infections in people who have already received a vaccine.
Adalja said: “Will this just push breakthroughs off to a later date? Is a second generation vaccination that creates more nasal immunity the actual solution to the breakthrough issues? The virus is always going to be here and I’m not sure chasing mild breakthroughs with intermittent boosters of first-generation vaccines is that valuable.”