Participate - St George's University Hospital

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Comparing COVID-19 Booster Vaccinations (COV-BOOST)  - Young Adults Fractional Dosing Sub-Study

What is the purpose of this research trial?

Young adults have a stronger immune response to vaccines than older adults, and results from the first stage of COV-BOOST and other COVID-19 vaccine studies have suggested that lower doses of BNT162b2 (Pfizer) or mRNA-1273 (Moderna) may give as good an immune response in young adults as higher doses. They may also be associated with fewer side effects or lower rates of already rare adverse events. Giving lower doses may also allow existing stocks of vaccines to be given to more people, which is important while need for the vaccine is greater than the number of doses available. This study is to evaluate the safety and side effect profile of giving lower doses of the Pfizer or Moderna COVID-19 vaccine to young adults, as well as assessing its impact on the immune response to the virus which causes COVID-19, called SARS-CoV-2.

We will be enrolling adults aged 18 to 30 years old who have had 2 or 3 doses of BNT162b2 (Pfizer) or mRNA-1273 (Moderna), are at least 6 months (180 days) after their last dose.

Am I suitable to take part?

You may be eligible to take part if you meet the following criteria:

  • You are 18-30 years old
  • You have received 2 or 3 doses of Pfizer or Moderna vaccine
  • You received your most recent dose at least 6 months ago
  • You have previously tested positive for COVID-19
  • You would be happy to not donate blood for the duration of the trial

For further details on why you could not take part in this study please see the Participant Information Sheet

Summary of the study

Participants will be randomised to receive one of the following:

  • BNT162b2 (Pfizer) vaccine (30mcg): this is the dose being used by the NHS.
  • BNT162b2 (Pfizer) vaccine (10mcg): this is one third of the normal dose and is the same as the dose being used in other countries for children aged 5 – 11 years.
  • mRNA-1273 (Moderna) vaccine (50mcg): this is the dose being used by the NHS as a 3rd dose booster.
  • mRNA-1273 (Moderna) vaccine (25mcg): this is one half of the dose of Moderna being used by the NHS as a 3rd dose booster.

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 four follow up visits to have blood tests to check for immune markers, and to check on the participants health.

Participants will initially be “blinded”, meaning they will not be told which vaccine they have been given until after they have attended a follow up visit 84 days after being vaccinated. If a participant is travelling prior to their day 84 follow up visit it may be possible to unblind them before the day 84 follow up visit if there is an urgent need and they have attended the follow up visit that is 28 days after vaccination

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?

If, at any time, after enrolment, you change your mind about being involved with this trial you are free to withdraw without giving a reason. Your decision will not result in any penalty. If you choose to withdraw from the trial, your standard medical care will not be affected.

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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