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Young Adults Fractional Dosing Sub-Study

Take part

Volunteers are needed for the latest COVID-19 vaccine booster study, launching in Southampton this week.


Researchers at University Hospital Southampton NHS Foundation Trust are leading the next phase of the COV-BOOST study, which is looking at the use of different COVID-19 vaccines and doses for giving a third dose in young adults.


The COV-BOOST: Young Adults Fractional Dosing Sub-study is looking for local volunteers who:

  • are between 18 to 30 years old

  • have had two doses of the Pfizer or Moderna COVID-19 vaccines, with at least 3 months (84 days) since their second dose

  • have not received a booster


The study is open to those who have previously tested positive for COVID-19, as well as those who have not tested positive for COVID-19 before.


Anyone interested in finding out more or taking part in the study can visit the COV-BOOST website, where they can complete the study questionnaire to see if they are eligible.


Participants will be reimbursed up to £225 for their time, inconvenience and travel, with boosters given in January and into February.


Young adults have a stronger immune response to vaccines than older adults, and results from COVID-19 vaccine studies have suggested that lower doses of the Pfizer or Moderna COVID-19 vaccines may give as good an immune response in young adults as higher doses. Lower doses may also be linked with fewer side effects or lower rates of already rare adverse events.


Using lower doses could allow existing stocks of vaccines to be given to more people, which is important while the need for vaccines is greater than the number of doses available globally.


Participants on the study will be randomly selected to receive one of the following doses:


  • A single dose of Pfizer (currently used in the UK booster programme)

  • One third of a single Pfizer dose (currently recommended for 5 - 11 years old in the UK)

  • A half Moderna dose (the dosage used by the NHS as a 3rd dose booster)

  • One quarter of a single Moderna dose


The study will take place at 15 hospitals across England, Wales and Scotland, and will include a total of over 900 participants. All participants will be monitored throughout the study for any potential side effects and will have bloods taken to measure their immune responses on the day of their first visit and then two weeks, one month, three months and eight months following vaccination.

All the trial sites are working on ways of including people in research from a wide variety of backgrounds and individuals from ethnic minorities are encouraged to apply.

How to take part

Volunteers can find out more about the study and sign up here: and

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