Following up first doses of the AstraZeneca or Pfizer vaccines with second doses of the Moderna or Novavax jabs generates a robust immune response against COVID-19, according to a study published in The Lancet journal.

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A team led by researchers at the University of Oxford in the UK found that no safety concerns were raised in the study of 1,070 participants. The study supports the flexible use of these vaccines in primary immunisation schedules, which is crucial to help rapidly deploy these vaccines, especially in low- and middle-income countries where vaccine supply may be inconsistent. "Thanks to studies such as these, we are now getting a more complete picture of how different COVID-19 vaccines can be used together in the same vaccine schedule," said Professor Matthew Snape, Associate Professor at the University of Oxford. "Encouragingly, all these schedules generated antibody concentrations above that of the licensed and effective two-dose Oxford-AstraZeneca schedule," said Snape, Chief Investigator on the trial.

When it comes to cellular immunity, the researchers said, having a first dose of the AstraZeneca vaccine followed by any of the other study vaccines generates a particularly robust response. In addition, a significantly higher number of short-lived vaccine reactions were reported in volunteers who received a second dose of Moderna compared to those who received two doses of either AstraZeneca or Pfizer.

Using different types of vaccines within the same schedule as we have done here (for example mRNA vaccines, viral-vector vaccines or protein-based vaccines) is a relatively novel approach to immunisation," Snape said.

"As well as providing evidence for flexibility in deployment, these results suggest this approach can also help generate better immune responses," he added. The researchers said the findings have implications beyond COVID-19 and will inform new approaches to immunisation against other diseases that are, as yet, not vaccine-preventable.