Source: Athit Perawongmetha/Reuters
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  • An Oxford study has found that a mix-and-match approach to COVID-19 vaccinations produce a stronger immune response
  • The highest antibody response was seen in people who received two doses of the Pfizer vaccine
  • However, an AstraZeneca shot followed by a Pfizer dose will produce a better response than if two AstraZeneca shots are given
  • While the findings offer greater flexibility in vaccination programs, there is not yet enough information to recommend a major shift in rollouts

According to an Oxford study published on Monday, a mixed schedule of COVID-19 vaccines — where a Pfizer shot is given four weeks after an initial AstraZeneca shot — will produce a stronger immune response than giving a second AstraZeneca dose.

Known as Com-COV, the study mixed two-dose programs of Pfizer and AstraZeneca vaccines and found that, in any combination, they produced higher concentrates of antibodies against the coronavirus spike protein.

The data provides support for a decision by some European countries, which have started offering alternatives to AstraZeneca as a second shot after it was linked to rare instances of blood clots.

Matthew Snape, the Oxford professor who led the trial, said the findings could be used to give flexibility to vaccination programs around the world, but added that there was not yet sufficient information to recommend a broader shift away from clinically approved schedules.

“It’s certainly encouraging that these antibody and T-cell responses look good with the mixed schedules,” he said.

“But I think your default has to stay, unless there’s a very good reason otherwise, to what is proven to work.”

The highest antibody response was seen in people who received two doses of the Pfizer vaccine, with both mixed schedules producing better responses than two doses of AstraZeneca’s shot.

An AstraZeneca shot followed by Pfizer produced the best T-cell responses, and also a higher antibody response than Pfizer followed by AstraZeneca.

The results were for combinations of vaccines given at four-week intervals to 830 participants, but Com-COV is also looking at mixed schedules over a 12-week interval, since the AstraZeneca shot is known to produce a better immune response with a longer interval between doses, according to Snape.

In Britain, officials have suggested an eight-week gap between vaccine doses for people over 40 and a 12-week gap for other adults.

“Given the UK’s stable supply position there is no reason to change vaccine schedules at this moment in time,” England’s Deputy Chief Medical Officer Jonathan Van-Tam said, adding that the data on a 12-week interval would influence future decisions regarding the country’s vaccine rollout.

More than 80 per cent of adults in Britain have now received one dose of a COVID-19 vaccine while 60 per cent have had two shots.

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