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Analysis: is it wise for England to mix and match Covid vaccines?

Postat la Jan 03, 2021

The UK is setting the pace around the world in the approval and use of Covid vaccines but, while other countries watch intently, not all are yet prepared to embrace what looks like public health pragmatism rather than strict adherence to evidence.

Britain is the first country in the world to approve and use the Oxford/AstraZeneca vaccine, just as it was first with Pfizer/BioNTech’s. In a further trailblazing decision, it is giving everyone a first shot of either of those vaccines, with the second shot delayed to 12 weeks afterwards instead of the three- or four-week interval in the trials.

And now it has emerged that NHS staff have permission, in limited circumstances, to mix and match the vaccines. With two different vaccines being used and supplies not guaranteed – particularly of Pfizer’s, which is in high demand around the world – the NHS in England has said people can be given a different second dose from the first, if absolutely necessary. So those who got the Pfizer jab first time around might – if supplies have run out (or if there is no record of which they had first) – be given the AstraZeneca version, says its Green Book for health staff on vaccine use. Scotland is following suit, although Wales says it will not.

But in the US in particular, which has already been critical of the UK approach to vaccines, there is scepticism.

Trials of the mix-and-match approach to boosters have not been done, although they are planned. In the New York Times, John Moore from Cornell University commented that British officials “seem to have abandoned science completely now and are just trying to guess their way out of a mess”.

The US Centers for Disease Control and Prevention has said that the authorised Covid-19 vaccines “are not interchangeable” and that “the safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product.”

The New York Times article sparked a transatlantic row, with the BMJ demanding a prominent retraction of a headline suggesting vaccine mix and match was officially approved. That was “seriously misleading”, said the BMJ editor, Dr Fiona Godlee.

It’s not official policy, said Dr Mary Ramsay, Public Health England’s head of immunisations. “We do not recommend mixing the Covid-19 vaccines – if your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa.”

But on the “extremely rare occasions” where the same vaccine is unavailable or it is unknown which jab the patient received, it is “better to give a second dose of another vaccine than not at all”.

That and the 12-week spacing are real-world responses to an epic crisis, in an attempt to give some immunity to the rampaging new variant of the coronavirus as quickly as possible to as many people as possible.

The US has had doubts about the UK approach already. Neither the US nor Europe is rushing to authorise use of the Oxford/AstraZeneca vaccine. Both seem to be waiting for more evidence from a large trial taking place in the US. Both were also sceptical of the UK’s rush to authorise the Pfizer vaccine, although they have also now done so. The US has also approved the Moderna vaccine, designed and made in the US, with substantial funding from Operation Warp Speed. It’s a similar vaccine to Pfizer’s and will help ramp up the vaccination effort.

Europe has given Pfizer’s vaccine emergency authorisation, whereas the faster procedure used by the Medicines and Healthcare products Regulatory Authority in the UK means that each batch must be assessed and certified as it is delivered. The same goes for Astra Zeneca’s vaccine, which is why the NHS has only 530,000 doses to use this week, out of the 4m promised.

The availability of vials and syringes around the world may also hold things up. As vaccines are approved and production speeds up, there will be increasing demand for these. It is possible that other countries too may be forced into pragmatic decisions like those of the UK.