A world-first study in the UK aiming to evaluate the safety and efficacy of mixing different COVID-19 vaccines has expanded to includes jabs developed by Moderna and Novavax.
The Com-Cov study, which has received £7m in UK government funding, was initially launched in February, becoming the first trial in the world to evaluate whether different vaccines can be used safely and effectively as part of two-dose regimens.
When the study first launched, the Department of Health and Social Care (DHSC) said that study participants could receive AstraZeneca (AZ)/Oxford University’s vaccine for their first dose and Pfizer/BioNTech’s vaccine for the second, or vice versa.
Following the trial expansion, participants may also now receive the Moderna or Novavax jab for their second dose.
The study will initially contain eight groups testing eight different combinations, with changes in vaccine dose order and time between doses.
The study is set to run for 13 months in total, although results from the first stage of the trial are expected next month, with the expanded trial potentially yielding reportable findings by June or July.
In addition to examining the safety and effectiveness of mixing different vaccines, researchers will also seek to gather immunological evidence on different intervals between vaccine doses for mixed-vaccine regimens compared to control groups using the same vaccine for both doses.
If the study is successful, the UK government may then consider reviewing the current vaccine approach, said the DHSC.
“Nothing will be approved for use more widely than the study, or as part of our vaccine deployment programme, until researchers and the regulator are absolutely confident the approach is safe and effective,” said Nadhim Zahawi, Minister for COVID-19 Vaccine Deployment.
Currently, the UK is implementing a same-dose regimen for the national COVID-19 vaccination drive, with no plans at the moment to make changes to the programme.
Professor Matthew Snape, chief investigator of the Com-Cov study, told BBC Radio 4 that mixing vaccines would “massively increase the flexibility and resilience of the immunisation programme and it will mean we can roll these vaccines out more quickly, not just in the UK but internationally”.
He added: “What I’m hoping is that we won’t rule out any combinations. 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?”