Could mixing Covid-19 vaccines be the perfect cocktail to speed up rollout?

Researchers say if vaccine combinations are proven to be as safe and effective as same-dose regimens, it could speed up the rollout globally and provide greater flexibility where supply issues arise
Could mixing Covid-19 vaccines be the perfect cocktail to speed up rollout?

Researchers at Oxford University are investigating whether ‘mixed-vaccine combinations’, such as giving one dose of the AstraZeneca vaccine followed by a second dose of the Moderna vaccine, will trigger the same immune response as two doses of the same vaccine. File picture:

UK researchers hope using different combinations of Covid-19 vaccines may help to speed up the vaccine rollout globally, as a University College Cork (UCC) scientist said the concept is not new, but requires further evidence.

Researchers at Oxford University are investigating whether ‘mixed-vaccine combinations’, such as giving one dose of the AstraZeneca vaccine followed by a second dose of the Moderna vaccine, will trigger the same immune response as two doses of the same vaccine.

The researchers say if vaccine combinations are proven to be as safe and effective as same-dose regimens, it could speed up the rollout globally and provide greater flexibility where supply issues arise.

The UK Com-Cov study has been expanded to test combinations of a first dose of the AstraZeneca or Pfizer vaccine with a second dose of either the Moderna or Novavax vaccines. 

Results from the study are expected in June or July, with some preliminary findings expected next month.

The research comes as blood clotting concerns linked with the AstraZeneca and Johnson & Johnson vaccines have led to their use being either restricted or paused.

UCC biochemist Dr Anne Moore said the concept of using two different vaccines in a two-dose regimen was not new but more evidence was needed before any ‘prime-boost’ combinations would be approved, although she noted France was already adopting this approach.

“The concept is definitely not new. But you need to know which vaccine is best for priming and which is best for boosting and we don’t know that yet,” Dr Moore told the Irish Examiner.

The Ebola vaccine, she said, was one example of a ‘prime-boost’ regimen, involving a Johnson & Johnson priming vaccine to trigger an immune response followed by a second vaccine by Bavarian Nordic as a booster. 

“That’s the only licenced vaccine regime that uses a different vaccine in the boost,” she said.

Dr Moore said people could have confidence in the science behind the vaccines and the clinical decisions being taken based on emerging evidence.

There was “no reason” not to give the second dose of the AstraZeneca vaccine, she said, as blood clotting incidents were not reported after the second dose in clinical trials.

It was also important to await the outcome of investigations in the US into the Johnson & Johnson single-dose vaccine before drawing any conclusions, she added.

“This is a dynamic situation and we need to be able to adapt to the evidence that is presenting and to move with that and to accept that these changes are about maintaining effectiveness and safety,” Dr Moore said, adding that there was also a “huge urgency” to get people vaccinated.

Speaking on RTÉ radio, Dr Moore said the possibility of extending the period between the first and second dose of the Pfizer vaccine may be a “pragmatic” approach to keeping the vaccine rollout moving, but said caution was also needed.

A single dose will provide some protection after two weeks, she said, adding there was US evidence to suggest the period between mRNA vaccine doses could be extended to six weeks, while the UK had adopted a longer interval period between doses.

“Both doses are required so that your immune system is boosted. As well as that not every person will respond after the first vaccination so the second vaccination is important for bringing those non-responders up to a responding level,” she said.

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