COVID19 vaccine: world first alternating dose trial underway in Birmingham

The world’s first COVID-19 vaccine study researching alternating doses and intervals of approved vaccines, is now underway in Birmingham.

The National Institute for Health Research (NIHR)-supported study, which will be run at BHP founder-member University Hospitals Birmingham NHS Foundation Trust, will determine the effects of using a different vaccine for the second dose to the first dose, in addition to two different intervals between doses.

The study, classified as an Urgent Public Health study by the NIHR, is being undertaken by the National Immunisation Schedule Evaluation Consortium (NISEC) and the Oxford Vaccine Group, and is backed by £7 million of government funding from the Vaccines Taskforce.

Over 800 volunteers, aged 50-years-old and above, are expected to take part in the study referred to as the COVID-19 Heterologous Prime Boost study, or ‘Com-Cov’, across eight sites across England – including in London, Birmingham and Liverpool.

The study, run at eight National Institute for Health Research (NIHR) supported sites, will 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.

A same-dose regimen is currently implemented for the national COVID-19 vaccination programme, and there are no current plans for this to change. Anyone who has received either the Pfizer or AstraZeneca vaccination as part of the UK-wide delivery plan will not be affected by this study. They will receive their second dose from the same source and over the same 12 week interval.

The clinical study will monitor the impact of the different dosing regimens on patients’ immune responses, and whether this can be a viable route to increase the flexibility of the UK’s vaccination programme. It has received ethics approval, as well as approval from the Medicines and Healthcare products Regulatory Agency (MHRA) to commence.

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).

Professor Jeremy Kirk, Clinical Director of the Clinical Research Network West Midlands said: ‘The more choices we have when it comes to vaccinating people, the greater our chances of finding a solution that suits everyone. This study will give us the data to make those decisions.”

The study will have eight different arms, testing eight different combinations and interval doses:

Oxford/AstraZeneca and Oxford/AstraZeneca – 28 days apart
Oxford/AstraZeneca and Oxford/AstraZeneca – 12 weeks apart
Pfizer/BioNTech and Pfizer/BioNTech – 28 days apart
Pfizer/BioNTech and Pfizer/BioNTech – 12 weeks apart
Oxford/AstraZeneca and Pfizer/BioNTech – 28 days apart
Oxford/AstraZeneca and Pfizer/BioNTech – 12 weeks apart
Pfizer/BioNTech and Oxford/AstraZeneca – 28 days apart
Pfizer/BioNTech and Oxford/AstraZeneca – 12 weeks apart

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.

Patients are to be recruited over the course of February via the NHS COVID-19 Vaccine Research Registry, with vaccinations expected to start towards the middle of the month and initial results to be made available over the summer period. The study will last for 13 months, and the UK public can volunteer to be contacted about taking part in the study and further COVID-19 vaccine studies by joining the registry or visiting website to find out more about the study and see if there is a study site near them.

If the study shows promising results, the MHRA would formally assess the safety and efficacy of any new vaccination regimen before it would be rolled out to patients.

Deputy Chief Medical Officer and Senior Responsible Officer for the study Professor Jonathan Van-Tam said: “Given the inevitable challenges of immunising large numbers of the population against COVID-19 and potential global supply constraints, there are definitely advantages to having data that could support a more flexible immunisation programme, if ever needed and approved by the medicines regulator.

“It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know.

“This study will be a promising opportunity to gain greater insight into how we can use the vaccines to stay on top of this nasty disease.”

The UK public can continue to support the national effort to speed up vaccine research and receive more information about volunteering for future vaccine studies by visiting

Please note: this study is separate to the COVID-19 national immunisation programme. Vaccines are not being mixed as part of the rollout of the national COVID-19 immunisation programme.