There have been limited cases of people receiving one coronavirus vaccine for their first dose, and a different vaccine for their second. So how will that affect their immunity? That's now the subject of a trial in the UK, seeking to discover whether a mix of vaccines proves effective against the virus. This has previously been done with vaccines for hepatitis, polio, and measles, mumps and rubella, per the BBC. "If we do show that these vaccines can be used interchangeably in the same schedule this will greatly increase the flexibility of vaccine delivery, and could provide clues as to how to increase the breadth of protection against new virus strains," the trial's chief investigator, Oxford University's Matthew Snape, tells CNBC. He notes mice have shown "a better antibody response with a mixed schedule rather than the straight schedule" of doses, per the BBC and Guardian.
About 800 English volunteers aged 50 and older will receive one of four different combinations of prime and booster shots from the Oxford-AstraZeneca and Pfizer-BioNTech vaccines. The Moderna vaccine may also be added to the 13-month trial this spring. Researchers will compare 4-week and 12-week dosing intervals. The UK generally administers doses 12 weeks apart, and an Oxford study published as a pre-print in the Lancet finds that a higher vaccine efficacy rate (82.4%) is obtained with an interval of at least 12 weeks between the first and second doses of the Oxford-AstraZeneca vaccine, compared to a lower rate (54.9%) with an interval of fewer than six weeks, per CNBC. The longer interval allows more people to be vaccinated with an initial dose. This research "will provide information vital to the rollout of vaccines in the UK and globally," Snape says. (Read more coronavirus vaccine stories.)