Adults are more likely to report mild and moderate side-effects after mixing doses of the AstraZeneca and Pfizer Covid vaccines, a study indicates.
Chills, headaches and muscle pain were reported more frequently when different vaccine doses were combined.Any adverse reactions were short lived, with no other safety concerns.
"It's a really intriguing finding and not something we were necessarily expecting," Prof Matthew Snape, from the Oxford Vaccine Group said.
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 Canadian provinces of Ontario and Quebec have both said they plan to mix vaccines in the near future.