A study evaluating a mix and match approach to COVID-19 vaccinations has found that using a different jab for the first and second doses gives good protection against the virus.

The Com-Cov study, announced earlier this year, is the first trial in the world to evaluate the effects of using different COVID-19 vaccines for the first and second dose within a two-dose vaccination regimen.

It is designed to monitor the impact of the different dosing regimens on immune responses. It is being run by the National Immunisation Schedule Evaluation Consortium (NISEC) across eight National Institute for Health Research (NIHR) supported sites.

Participants were given either the standard two doses of the AstraZeneca/Oxford University or Pfizer/BioNTech vaccines or a combination of the two.

Researchers found that both mixed schedules induced high antibody levels against the SARS-CoV-2 virus when doses were administered four weeks apart.

However, they also discovered that the order of the vaccines made a difference. Specifically, administering the AZ/Oxford vaccine followed by the Pfizer/BioNTech jab induced higher antibodies and T-cell responses compared to Pfizer/BioNTech followed by a dose of the AZ/Oxford vaccine.

The protection against COVID-19 offered by both of these regimens was also higher than the licensed two-dose AZ/Oxford vaccine schedule.

The highest antibody response was observed after the two-dose Pfizer/BioNTech vaccine schedule, with the highest T cell response seen with a first dose of the AZ/Oxford vaccine followed by Pfizer/BioNTech.

‘We know that the Oxford-AstraZeneca two-dose schedule is highly effective and has helped to save many lives,” said Andrew Ustianowski, NIHR clinical lead for the COVID-19 vaccination programme and joint national infection specialty lead

“The fact we now know it works well, in terms of immune responses, when combined with the Pfizer vaccine provides researchers with the valuable knowledge that these vaccines could be used flexibly for those yet to be vaccinated in the UK and globally,” he added.