The University of Oxford in the UK is set to initiate the first trial to analyse the feasibility of using a different Covid-19 vaccine for the initial ‘prime’ vaccination to the follow-up ‘booster’ vaccination.

Run by the National Immunisation Schedule Evaluation Consortium (NISEC), the study is backed by £7m government funding from the UK Vaccines Taskforce.

Referred to as the COVID-19 Heterologous Prime Boost study (Com-Cov), the trial will enrol over 800 participants aged 50 years and above from eight sites in England. It will be supported by the National Institute for Health Research (NIHR) to analyse four different combinations of prime and booster vaccination.

The combinations are: a first dose of the Oxford-AstraZeneca vaccine followed by a booster with either the Pfizer vaccine or another dose of Oxford-AstraZeneca vaccine, or a first dose of the Pfizer vaccine followed by booster dose with either Oxford-AstraZeneca vaccine or Pfizer vaccine.

The vaccines will be analysed at a four-week interval for an early interim data readout, and at a 12-week interval for comparison to present UK policy.

In the 13-month study, blood samples collected from the participants will be analysed to monitor different dosing regimens’ impact on immune responses of the participants and for any additional adverse reactions to the new combinations.

University of Oxford Paediatrics and Vaccinology associate professor trial’s chief Investigator Matthew Snape said: “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.

“This is a tremendously exciting study that will provide information vital to the roll out of vaccines in the UK and globally.”

If the study produces promising results, the UK Medicines and Healthcare products Regulatory Agency (MHRA) would formally evaluate the safety and efficacy of any new vaccination regimen before rolling out for use in patients.