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World's first COVID-19 vaccine alternating dose study launches in Oxford

World's first COVID-19 vaccine alternating dose study launches in Oxford

The world’s first COVID-19 vaccine study researching alternating doses and intervals of approved vaccines has opened in Oxford.

The LCRN-supported study 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.

It is seeking 100 volunteers aged 50 and over for the trial at the University of Oxford’s Centre for Clinical Vaccinology and Tropical Medicine at the Churchill Hospital.

Over 800 volunteers are expected to take part in the COVID-19 Heterologous Prime Boost study, or ‘Com-Cov’, across eight UK sites.

Patients will be recruited during February via the NHS COVID-19 Vaccine Research Registry, where people sign up to be told about COVID-19 vaccine studies they could take part in.

Vaccinations are expected to start towards the middle of the month and initial results made available in the summer. For more information visit www.comcovstudy.org.uk.

The study 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 the Pfizer or AstraZeneca vaccination will not be affected.

The 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.

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).

Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, said: “This is a tremendously exciting study that will provide information vital to the roll out of vaccines in the UK and globally. 

“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.”

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

  • Oxford/AstraZeneca and Oxford/AstraZeneca - 28 days apart
  • Oxford/AstraZeneca and Oxford/AstraZeneca - 12 weeks apart - as a control group
  • Pfizer/BioNTech and Pfizer/BioNTech - 28 days apart
  • Pfizer/BioNTech and Pfizer/BioNTech - 12 weeks apart - as a control group
  • 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.

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.