A new clinical trial has been launched in the UK to study whether patients receiving different COVID-19 vaccines for their first and second dose is effective. 

The trial is backed by ￡7 million of government funding and will be the first in the world of its kind to determine the effects of using different vaccines – for example, using Oxford University/AstraZeneca’s vaccine for the first dose, followed by Pfizer/BioNTech’s vaccine for the second.

The study, run by the National Immunisation Schedule Evaluation Consortium (NISEC) across National Institute for Health Research (NIHR) supported sites, will also gather immunological evidence on different intervals between the first and second dose for a mixed-vaccine regimen against control groups when the same vaccine is used for both doses.

The 13-month study will monitor the impact of the different dosing regimens on patients’ immune responses, which have the potential to be higher or lower than from the same dose regimen. Initial findings are expected to be released in the summer. Vaccinations are expected to start towards the middle of February. 

Should the study show promising results, then the government may consider reviewing the vaccine regimen approach if needed, but only if proven to be safe and recommended by the Joint Committee on Vaccination and Immunisation (JCVI).

Minister for COVID-19 Vaccine Deployment, Nadhim Zahawi, said: “This is a hugely important clinical trial that will provide us with more vital evidence on the safety of these vaccines when used in different ways. 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.”

The study will initially have eight different arms testing eight different combinations, but more products may be added. The arms include:

• two doses of the Oxford/AstraZeneca vaccine at 28 days apart

• two doses of the Oxford/AstraZeneca vaccine at 12 weeks apart – as a control group

• two doses of the Pfizer/BioNTech vaccine at 28 days apart

• two doses of the Pfizer/BioNTech vaccine at 12 weeks apart – as a control group

• the Oxford/AstraZeneca vaccine for the first dose, followed by the Pfizer/BioNTech vaccine for the second, at 28 days apart

• the Oxford/AstraZeneca vaccine for the first dose, followed by the Pfizer/BioNTech vaccine for the second, at 12 weeks apart

• the Pfizer/BioNTech vaccine for the first dose, followed by the Oxford/AstraZeneca vaccine for the second, at 28 days apart

• the Pfizer/BioNTech vaccine for the first dose, followed by the Oxford/AstraZeneca vaccine for the second, at 12 weeks apart. 

Over 800 patients are expected to take part in the study, referred to as the COVID-19 Heterologous Prime Boost study or ‘Com-Cov’, across eight different sites across England.