UK study says safe to mix Pfizer and AstraZeneca doses

A study released yesterday (28 June) found that it would be safe to mix Pfizer and AstraZeneca doses, which could speed up UK vaccine roll-out if adopted

The study is currently in preprint form, waiting to be published by The Lancet. In February, the Com-COV study began. A group of scientists ran tests, combining Pfizer and AstraZeneca doses to see if the overall efficacy would be as good as if two doses of one vaccine were given.

Dr Matthew Snape, University of Oxford, said: “Any of these schedules, I think could be argued, would be expected to be effective.”

The average age of participants was roughly 57 years old, with 45.8% female and then a further 25.3% from ethnic minorities. Overall, 830 people participated in this study.

So, did the mixed doses work better?

In some cases, yes.

Though the findings of the com-COV trial are yet to be peer-reviewed, the team found that two doses of Pfizer was still one of the best for generating antibodies. Interestingly, they found that mixing one dose of Pfizer with AstraZeneca created more antibodies than two doses of AstraZeneca.

For instance, those who first took Pfizer then AstraZeneca had five times more antibodies than people with a double-dose of AstraZeneca. But those who got AstraZeneca first, followed by Pfizer, had antibody levels as high as if they got two doses of Pfizer.

It is not currently known why mixing Pfizer with anything else creates more antibodies, but the team at Oxford University will now conduct another mixing trial to find out if similar things happen with Moderna and Novavax.

Will adopting this policy speed-up rollout in the UK?

Only if there’s a shortage of one vaccine, which can happen. In that case, allowing mixing of vaccines would mean that more people can get their second dose as soon as possible.

However, the real issue remains in the people who have no vaccine access. Some countries are barely 3% vaccinated, due to a lack of access to doses. These places in the Global South are at huge risk of further waves, that both devastate their populations and create new variants.