Scientists test the risks and rewards of mixing Covid shots

Oxford scientists are expanding efforts to test whether two different Covid-19 vaccines can be combined, after some European countries worried by rare side effects with the Oxford/AstraZeneca jab started offering other vaccines as second shots. For the second stage of its continuing trial, the Oxford Vaccine Group is recruiting more than a thousand participants who have already received an AstraZeneca or BioNTech/Pfizer shot. The group of over-50s will either receive a second dose of the same vaccine or get a dose of the Moderna or Novavax shots. Matthew Snape, associate professor in paediatrics and vaccinology at Oxford, said the study could mean that people do not become “hostage to fortune” when there are supply shortfalls or changes to recommendations on who should take which vaccine.