Pfizer boosters show 95.6% efficacy against Covid, study finds

A booster shot of the BioNTech/Pfizer vaccine is 95.6 per cent effective against Covid-19 compared with two shots and a placebo, the companies said on Thursday, citing preliminary results from the first randomised, controlled trial on boosters.

Ugur Sahin, the head of BioNTech, said the “important data” added to the body of evidence suggesting that a booster dose could help “protect a broad population of people from this virus and its variants”.

“Based on these findings, we believe that, in addition to broad global access to vaccines for everyone, booster vaccinations could play an important role in sustaining pandemic containment and a return to normalcy,” he said.

In a trial with 10,000 participants who had all completed a two-shot Pfizer regimen, half were randomised to receive a further equal-strength dose of the shot, and half a placebo. Five cases of Covid were registered in patients receiving the booster compared with 109 who were given a placebo.

The trial took place during a period when the Delta coronavirus variant was prevalent, and the median time between second and third doses was about 11 months, with a median follow-up time of two-and-a-half months.

Andy Hill, a senior visiting research fellow in pharmacology at the University of Liverpool, said the trial was “very important” because it provided a “much stronger” level of evidence.

“It is randomised and measures effects on new infections. This is a big step forwards from previous studies of other vaccines which only measured effects on antibody levels,” Hill said. “This new trial is much more reliable.”

However, it remains to be seen how long a booster can protect for, when “antibody levels wax and wane”, said Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.

“Will this just push breakthroughs [infections post vaccination] off to a later date? Is a second generation vaccination that creates more nasal immunity the actual solution to the breakthrough issues?” Adalja said. “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.”

The median age of participants was 53, with little more than half in the 16 to 55 age group. More than a fifth were older than 65, a category more at risk from severe Covid. Multiple subgroup analyses, the companies noted, showed that relative efficacy was “consistent” regardless of age, sex, race, ethnicity or other underlying conditions.

The safety profile of the vaccine was “generally consistent” with other data available, the companies said, adding that they would share the information with US, EU and other regulatory agencies.

Marco Cavaleri, the head of the European Medicines Agency’s vaccines strategy division, said the agency would be evaluating the data as part of a broader assessment of boosters.

While he declined to comment directly on the study, which has not yet been peer-reviewed, he told reporters on Thursday that the review was “quite important” in informing vaccination campaigns.

The debate around boosters has been fractious, dividing the scientific community this year as companies including Pfizer and BioNTech said protection afforded by their vaccines waned over time, especially against Covid caused by the Delta variant. Crucially, however, no booster data from randomised control trials, the gold standard in drug research, had been available before Thursday.

The US Food and Drug Administration on Wednesday gave the green light to mix-and-match boosting, allowing any US citizen at high risk of contracting Covid to receive a further shot of any approved vaccine.

High-income countries, including Israel, the UK, US and EU nations, have begun rolling out boosters to their populations to ensure they remain protected throughout winter, when transmission is aided by indoor mixing.

For comparison, vaccination rates in lower-income nations consistently lag behind: only 2.8 per cent of those living in these countries have received at least one shot.

Additional reporting by Jamie Smyth in New York