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Comparing COVID-19 Booster Vaccinations (COV-BOOST)  - Bivalent Omicron Fourth Dose Booster Sub-Study

What is the purpose of this research trial?

The Omicron variant is now the most common variant of the virus which causes COVID-19 (SARS-CoV-2) in the UK, and due to mutations on its spike protein it is more capable of evading the immune response generated by existing vaccines against COVID-19 than previous variants.

This study is trying to determine the side effect profile, safety and immune response of giving different fourth COVID-19 vaccine booster doses of BNT162b2 (Pfizer) and a bivalent vaccine, mRNA-1273.214 (Moderna) to people who have previously received 3 doses of COVID-19 vaccine. We will be enrolling participants aged 30 years or older who have received 3 doses of COVID-19 vaccine (with the third dose being either BNT162b2 or mRNA-1273) and are at least 3 months (84 days) after their third dose.

What are the vaccines against?

These vaccines are against the coronavirus SARS-CoV2 that causes the disease COVID-19.

Am I eligible to take part?

If you meet the following criteria, you could be eligible to take part. Please complete our screening questionnaire at the bottom of the page if you would like to see if you are eligible and submit your contact details.

  • You are aged 30 years or older
  • You have had 3 doses of a COVID-19 vaccine and you received mRNA1273 (Moderna) or BNT162b2 (Pfizer) as your third dose
  • You had your third dose of COVID-19 vaccine at least 3 months ago
  • You have not tested positive for COVID-19 in the last 3 months (84 days)
  • You must be willing to tell the trial staff about your medical history
  • If you are able to become pregnant you must be willing to practice continuous effective contraception during the first 3 months of the trial and have negative pregnancy tests on the day of vaccination
  • You must agree not to donate blood during the trial

For further details on the eligibility criteria for this study please see the Participant Information Sheet.

Summary of the study

We are studying the use of a new COVID-19 vaccine given as a fourth dose booster, compared to a dose of BNT162b2 (the Pfizer COVID-19 vaccine). The pharmaceutical company Moderna which produced the mRNA-1273 vaccine for COVID-19, has adapted it and made a new vaccine (mRNA-1273.214) which contains 2 versions of the spike protein (because it has 2 versions, it is called a “Bivalent” vaccine). One of these is the original version of the spike protein found in the widely used COVID-19 vaccines, based on the originally circulating form of the virus. The other is a version of the spike protein which more closely resembles the one found on Omicron.

This study is to evaluate the safety and side effect profile of giving a dose of mRNA-1273.214 compared to BNT162b2 COVID-19 vaccine to healthy adults, as a fourth dose COVID-19 booster, as well as assessing its impact on the immune response to different variants of SARS-CoV-2, including the Omicron and Delta variants.

Participants will be randomised to receive either a dose of the BNT162b2 (Pfizer) vaccine or a dose of the mRNA-1273.214 vaccine. Participants will be “blinded”, meaning they will not be told which vaccine they have been given until after they have completed the study. They will then complete a diary of their symptoms over the next 7 days, and any other adverse events which occur up to 3 months after having had the vaccine. There are several follow up visits to have blood tests to check for immune markers, and to check on the participants health.

What are the advantages of taking part?

We anticipate that participating in the trial will mean that you gain some additional protection against the coronavirus. Most importantly, the information gained from the trial will make a valuable contribution to the pandemic response.

Are there any risks from taking part in the study?

Vaccines, like all medicines, can have side effects. These are usually minor (such as a sore arm) and usually last only a few days. More serious side effects are rare, and we will discuss these with you in more detail if you might wish to participate. The blood samples taken in the study may cause slight pain and occasionally bruising.  Please refer to the participant information sheet for full details of procedures and potential risks.

What will happen if I don’t want to carry on with the trial?

Participation is voluntary and you are free to change your mind and withdraw at any time. You do not need to provide a reason. This would not affect your subsequent medical care in any way.

Is reimbursement provided for taking part in this trial?

Yes. Participants will be reimbursed for their time, travel and inconvenience, up to £225 based on the number of visits that they attend.

What’s next?

If you would like to find out more, please read the Participant Information Sheet and if you are interested in taking part, please complete our pre-screening questionnaire.


   Download the Participant Information Sheet (PDF)

Please note : This site is not currently recruiting

  Complete the Pre-screening Questionnaire


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