A study has been found that adults are more likely to report mild and moderate side-effects after mixing doses of the AstraZeneca and Pfizer Covid vaccines.
The “Com-COV” study has been said to be the “world-first” by the U.K. government and led by the University of Oxford. It is examining the immune responses of trial participants given a dose of the Oxford-AstraZeneca vaccine followed by the Pfizer-BioNTech shot — and vice versa.
Chills, headaches and muscle pain were reported more frequently when different vaccine doses were combined. Any other adverse reactions were short-lived, with no other safety concerns.
The Com-Cov study launched in February to see whether a different jab for the second dose might give longer-lasting immunity, better protection against new variants or simply allow clinics to swap vaccines if supplies are interrupted.
The study didn’t point to any safety issues and the stronger side effects vanished after a few days. The results suggest, however, that mixed dose schedules could result in an increase in work absences the day after immunization.
In France, people who got the first dose of the Astra vaccine before the government restricted it to older patients are being offered the vaccine developed by Pfizer and BioNTech SE for their second injection.
The Canadian provinces of Ontario and Quebec have both said they plan to mix vaccines in the near future, amid uncertainty over shipments of the Oxford-AstraZeneca jab and concerns about rare blood clots.
In a peer-reviewed research letter published in The Lancet international medical journal, researchers of the trial reported that when given at a four-week interval, both of the alternating vaccine schedules of the Oxford-AstraZeneca vaccine and the Pfizer-BioNTech vaccine induced more frequent reactions following the second dose than the standard non-mixed schedules.
“Whilst this is a secondary part of what we are trying to explore through these studies, it is important that we inform people about these data, especially as these mixed-doses schedules are being considered in several countries,” Matthew Snape, associate professor in Paediatrics and Vaccinology at the University of Oxford, said in a statement.