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United Kingdom is Alternating Different COVID-19 Vaccines Between First and Second Doses

The UK announced it is beginning a 2-dose study using one dose of the Pfizer/BioNTech and one dose of AstraZeneca in each individual participant.

The United Kingdom announced today its launching a study designed to give participants either the Pfizer/BioNTech or the AstraZeneca COVID-19 vaccine for the first dose and then alternating the other vaccine for the boost shot.

This would be the first study in the world to look at using these 2 different vaccines for each study participant.

“Given the inevitable challenges of immunizing large numbers of the population against COVID-19 and potential global supply constraints, there are definite advantages to having data that could support a more flexible immunization program, if needed,” Jonathan Van-Tam, MBE, deputy chief medical officer for England, said. Van-Tam was appointed to the expert advisory group for the UK Government's Vaccine Taskforce last year.

The study is called the COVID-19 Heterologous Prime Boost study or “Com-Cov.” It is looking to gather over 800 participants and will use 8 sites across England.

The study will initially have 8 different arms testing 8 different combinations, but more products may be added. The 8 arms include:

  • 2 doses of the Oxford/AstraZeneca vaccine at 28 days apart
  • 2 doses of the Oxford/AstraZeneca vaccine at 12 weeks apart–as a control group
  • 2 doses of the Pfizer/BioNTech vaccine at 28 days apart
  • 2 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

The study, run by the National Immunization Schedule Evaluation Consortium (NISEC) across 8 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 as early as June of this year.

The study has received ethics approval from the Research Ethics Committee, as well as approval from the Medicines and Healthcare products Regulatory Agency (MHRA).