The UK is expanding its Com-Cov study, a major trial on mixing different types COVID-19 vaccines used for first and second doses, BBC News online reported on Wednesday.

People aged 50 and above who have received a first dose of the Pfizer or AstraZeneca vaccine can now take part in the Com-Cov study. Their second dose could be the same again, or a Moderna or Novavax vaccine.

The study will run for a year and results of the first stage are expected in May, with reportable findings from the expanded trial expected by June or July 2021.

Reportedly, a combination of vaccines may give broader, longer-lasting immunity against COVID-19 and new variants of it. This will also provide more flexibility to the vaccine rollout.

Prof Matthew Snape, from the Oxford Vaccine Group and chief investigator on the trial, was quoted as saying that he hoped to recruit 1,050 volunteers who had already received one dose on the NHS in the past eight to 12 weeks. Over 800 people are already taking part in the research and have received two doses of either Pfizer, AstraZeneca or a mix.