Intended for healthcare professionals


US and Canada to roll out the first omicron specific boosters within days

BMJ 2022; 378 doi: (Published 02 September 2022) Cite this as: BMJ 2022;378:o2144
  1. Owen Dyer
  1. Montreal, Canada

Coronavirus vaccine booster shots reformulated to combat the latest strains of the omicron variant will be available across the US within a few days—the first vaccines offered to target a strain other than the original virus detected in 2019.

The Food and Drug Administration (FDA) authorised updated boosters from Pfizer BioNTech and from Moderna on 31 August, and an expert advisory committee convened the next day by the Centers for Disease Control and Prevention (CDC) voted 13-1 to recommend their use. CDC director Rochelle Walensky endorsed the committee’s decision that evening.

The Pfizer booster is authorised for use in people aged 12 and over, and Moderna’s for those over 18. Both will be offered to all eligible age groups immediately. The old formulations were simultaneously de-authorised for use as boosters, though they remain the mainstay of initial vaccination. The FDA expects to authorise the new boosters in younger age groups before the year’s end.

The boosters’ efficacy has not yet been tested in humans in a controlled trial. Instead, after omicron BA.4 and BA.5 spike proteins were added to the original vaccine, the new formulation was shown to increase antibodies to those strains in mice. The booster is a bivalent vaccine, since it targets both omicron and the original SARS-Cov2 strain.

Some experts expressed disquiet about the lack of human trials, and some suggested that it might be seized on by vaccine opponents to spread doubt about the boosters’ safety.

The lone “no” vote on the CDC expert panel, Pablo Sanchez, professor of paediatrics at Ohio State University, said at the meeting that he was “struggling with making a recommendation for a bivalent vaccine that has not been studied in humans.”

The panel was provided with human safety data from trials of previous Pfizer and Moderna bivalent boosters that were designed to tackle the omicron BA.1 variant. Moderna’s BA.1 booster was authorised in Canada on the day the CDC panel met.

Several panellists noted that the process used by the FDA to authorise the new omicron boosters was similar to that used for each year’s reformulated flu vaccine, which also relies heavily on animal studies.

Most said that the decisive factor behind their recommendation to proceed was the approach of autumn, when people will spend more time indoors and cases are expected to rise. The US is already seeing nearly 500 deaths a day.

A projection shown to the experts estimated that waiting to roll out the new boosters until November, when more human data will be available could have resulted in 9700 more deaths and 137 000 more hospital admissions.1

Canada approves older omicron booster

Health Canada on 1 September approved for adults Moderna’s bivalent booster that targets the omicron BA.1 variant. BA.1 disappeared from circulation in May, but Canada’s National Advisory Committee on Immunization said the new booster will generate a significantly more effective neutralising antibody response against BA.4 and BA.5 than the original Moderna vaccine. Pfizer’s BA.1 booster has not yet passed Canadian review.

The UK has also approved Moderna’s bivalent booster targeting the BA.1 variant,2 while the European Medicines Agency has authorised both Moderna’s and Pfizer’s BA.1 based boosters.3

Pfizer and Moderna have not yet submitted their newest boosters for Canadian approval, but are expected to do so in the next two weeks. Canadians were urged, however, not to wait but to get boosted now.

Canada has 780 000 BA.1 boosters on hand but expects 10.5m more towards the end of September. The US has already bought 170m of the newer BA.4 and BA.5 boosters, which should be widely available after 5 September.

The boosters may be taken with a flu shot. But people who recently received one of the older boosters should wait at least two months before getting the new shot, the CDC said, to maximise efficacy and reduce the chance of side effects.

People who have recently received the monkeypox vaccine Jynneos are advised to wait four weeks before getting a coronavirus booster, to minimise the chance of pericarditis, the most common significant adverse effect of mRNA coronavirus vaccines. But people who have recently been boosted against covid should follow medical advice recommending monkeypox inoculation if they are exposed to that virus, or if that outbreak worsens, the CDC advised.

The CDC will be closely tracking the real world impact of the new boosters to see if they match projections, FDA commissioner Robert Califf told journalists. “The proof will be in the pudding,” he said.

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