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UK study shows mixing Pfizer and AstraZeneca COVID-19 vaccines with Moderna elicits better immune response

Results show support in favour of heterologous dosing which may help to advance vaccination programmes in poorer countries.

A British study mixing COVID-19 vaccines has found that people had a better immune response when they received their first dose of AstraZeneca or Pfizer-BioNTech shots, followed by Moderna nine weeks later, according to Reuters.

These results support mix-and-match dosing, otherwise known as heterologous dosing. This is expected to boost vaccine drives in poor and middle-income countries, which may need to combine different brands between first and second shots if supplies are running low.

Matthew Snape, the Oxford professor behind the study dubbed Com-COV2, said: “We found a really good immune response across the board…, in fact, higher than the threshold set by Oxford-AstraZeneca vaccine two doses. I think the data from this study will be especially interesting and valuable to low- and middle-income countries where they’re still rolling out the first doses of vaccines.”

The study of 1,070 volunteers also found that a dose of the Pfizer-BioNTech vaccine, followed by a Moderna jab, was more effective than two doses of the standard Pfizer-BioNTech course.

Snape added: “We’re showing…you don’t have to stick rigidly to receiving the same vaccine for a second dose…and that if the programme will be delivered more quickly by using multiple vaccines, then it is okay to do so.”

Clinical studies of the Moderna vaccine have shown that antibody levels remain strong after six months, but studies after the six-month mark have had mixed responses. Reports of waning antibody levels after two doses have added to the evidence that a booster strategy is essential. The increasing threat of the prolific Delta and Omicron variants have also ramped up the pressure to accelerate vaccination campaigns.