Another Study Supports Mixing Vaccine Doses

Published in The Lancet, University of Oxford-based study has found that mixing and matching AstraZeneca and Pfizer vaccines “induced high concentrations of antibodies.” The combination of doses, taken 28 days apart, triggered a superior immune response to two doses of the AstraZeneca vaccine.

Professor Snape, chief investigator on the study, said, “The Com-COV study has evaluated ‘mix and match’ combinations of the Oxford and Pfizer vaccines to see to what extent these vaccines can be used interchangeably, potentially allowing flexibility in the UK and global vaccine roll-out.” The trial recruited 830 volunteers over the age of 50 from various sites across England.

An intriguing finding from the Oxford study was that there is a difference in immune response depending on which vaccine is given first. The antibody response was superior for those who received AstraZeneca then Pfizer, while T-cell response was greater for Pfizer first then AstraZeneca.

The European Medicines Agency discussed the Oxford findings in a press conference last Thursday. According to the agency, the study along with “preliminary results from studies conducted in Spain and Germany … show that this strategy achieves satisfactory immune response and no safety concerns.”

The findings suggest that booster shots based on one vaccine could be given to those who initially received a different vaccine. The study is proceeding to investigate combinations including Moderna and Novavax. 

The studies were set up because some European countries have already been giving people a second dose of Pfizer after having received a first dose of AstraZeneca, due to safety concerns relating to blood clots. For the same reason, it is of interest to Australians who received a first dose of AstraZeneca and may wish to get a second dose of Pfizer, with the government now promising a supply of 2 million doses per week from October.

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