A U.K. study analysing how safe it is to administer different types of Covid-19 vaccine for the first and second dose has been expanded.
The Com-Cov study was first launched in February to explore the idea of alternating the Oxford/AstraZeneca and Pfizer/BioNTech vaccines, and this has now been extended to include the Moderna and Novavax vaccines.
Experts are looking into whether mixing vaccines may give more effective and longer-lasting protection against coronavirus and any new variants that emerge. This would also give greater flexibility when it comes to administering the second dose of a vaccine.
"The focus of both this and the original Com-Cov study is to explore whether the multiple Covid-19 vaccines that are available can be used more flexibly, with different vaccines being used for the first and second dose," explained Professor Matthew Snape, chief investigator on the trial from the University of Oxford. "If we can show that these mixed schedules generate an immune response that is as good as the standard schedules, and without a significant increase in the vaccine reactions, this will potentially allow more people to complete their Covid-19 immunisation course more rapidly.
"This would also create resilience within the system in the event of a shortfall in the availability of any of the vaccines in use."
The University of Oxford-led study is now looking for 1,050 adults aged over 50 who have received their first vaccination in the past eight to 12 weeks.
Participants will have received either the AstraZeneca or Pfizer vaccine first and will then be randomly selected to receive either the same type of vaccine for their second dose or a dose of Moderna, which has just started rolling out in the U.K., or Novavax, which is being reviewed by the Medicines and Healthcare products Regulatory Agency (MHRA).
Scientists will look for any adverse reactions and study how the immune system reacts to combinations of vaccine.
Results from the second part of the study are expected in June or July.
"What I'm hoping is that we won't rule out any combinations," Professor Snape said. "That's how we need to look at it - are there any combinations we shouldn't be giving because they don't generate a good immune response, and I'm hoping that won't be the case."
More than 800 people have already enrolled to take part in the first part of the study and received two doses of either AstraZeneca, Pfizer, or a mix.