Mixing Covid vaccines generates robust immune response, study finds

First doses of the Oxford/AstraZeneca or Pfizer/BioNTech coronavirus vaccines followed by second doses of the Moderna or Novavax jabs will generate stronger immune responses against Covid-19, researchers have found.

According to the study, participants who received a first dose of the Oxford or Pfizer jab generated a robust immune response when given a second dose of vaccines manufactured by Novavax or Moderna nine weeks later.

No safety concerns were raised in this study of 1,070 participants, the University of Oxford-led Com-COV study found.

Listen to our coronavirus podcast:

Researchers say the study supports the flexible use of these vaccines in primary immunisation schedules, which is crucial to help their rapid deployment especially in low-and middle-income countries where vaccine supply may be inconsistent.

Matthew Snape, associate professor in paediatrics and vaccinology at the University of Oxford, and chief investigator on the trial, said: “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.

“Encouragingly, all these schedules generated antibody concentrations above that of the licensed and effective two-dose Oxford/AstraZeneca schedule.

“When it comes to cellular immunity, having a first dose of the Oxford/AstraZeneca vaccine followed by any of the other study vaccines generates a particularly robust response”.

The research found that both Oxford followed by Moderna/Novavax schedules both induced higher antibodies and T-cell responses than the licensed and highly effective standard two-dose Oxford schedule.

Pfizer/Moderna induced higher antibody and T-cell responses than the standard two-dose Pfizer schedule.

And Pfizer/Novavax induced higher antibodies than the two-dose Oxford schedule which induced lower antibody and T-cell responses than the two Pfizer doses.

Researchers also looked at the vaccine responses to different coronavirus variants.

Blood samples taken from participants were tested for their effectiveness against the Wild-Type, Beta and Delta variants.

While it was observed that the vaccines’ efficacy against the variant strains had decreased, this was a consistent trend across the mixed schedules.

The study, published in The Lancet, also found that 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 the Oxford or Pfizer jabs.