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FAQ section on vaccinations

What is the difference between a 3rd primary dose vaccine and a booster?

A 3rd primary dose is offered to individuals who may not have mounted a full immune response to 2 doses of COVID-19 vaccine because they are immunosuppressed due to an underlying health condition or drug treatment. For those aged 18 years the JCVI advises a preference for mRNA vaccines Pfizer or Moderna. For those aged 12 to 17 years the Pfizer-BNT162b2 vaccine remains the preferred choice. The third primary dose should ideally be given at least 8 weeks after the second dose.

In contrast booster doses are given to maintain protection against COVID-19 disease as this wanes over time. The JCVI advises a preference for the Pfizer vaccine to be offered as the third booster dose irrespective of which vaccine was used for doses 1 and 2. Alternatively, individuals may be offered a half dose of the Moderna vaccine. Currently booster vaccines are only offered to:

  • those living in residential care homes for older adults

  • all adults aged 50 years or over

  • frontline health and social care workers

  • all those aged 16 to 49 years with underlying health conditions that put them at higher risk of severe COVID-19 (but are not eligible for a 3rd primary dose), and adult carers

  • adult household contacts (aged 16 or over) of immunosuppressed individuals

The booster vaccine dose is offered no earlier than 6 months after completion of the primary vaccine course

Further advice:

3rd primary doses: Joint Committee on Vaccination and Immunisation (JCVI) advice on third primary dose vaccination - GOV.UK (

Booster doses: JCVI statement regarding a COVID-19 booster vaccine programme for winter 2021 to 2022 - GOV.UK (

I have just been given a 3rd primary dose, and have now been offered a booster as well - do I need to have both to get adequate protection?

No, you are advised to have a 3rd primary dose OR the booster.  For most participants this is likely to involve vaccination with the Pfizer vaccine irrespective of whether you receive a 3rd primary dose or the booster. The only difference is that a 3rd primary dose will be offered earlier than a booster. 

Should my vaccination be timed around the dates of my biologic infusion or injection?

The main priority with timing is to receive a 3rd dose as soon as you are eligible. If you are switching to a new biologic treatment and have not yet received a first dose then talk to your IBD team about delaying this dose until 2 weeks after a 3rd vaccine dose.   

I had undetectable levels of antibodies after my second vaccine dose and have since received a 3rd dose. What antibody response do you expect after a 3rd dose?

Firstly, recent data from CLARITY IBD has shown that almost all breakthrough SARS-CoV-2 infections after 2 doses of vaccination are mild, even in people with low antibody levels. Secondly, data from a number of studies have shown that the majority of patients have a good antibody response after a 3rd vaccine dose, even if antibody levels were low or undetectable after 2 doses. However, the durability of antibody responses after 3 doses in not yet know.

I participated in the sub study of CLARITY and my blood was taken for T- Cell work, will I be able to have access to these results

No, unfortunately we cannot release these results currently. This is because the T-cell responses which correlate with protection against SARS-CoV-2 infection, symptomatic disease and severe COVID-19 are not known. Therefore, we do not know what level of T-cell response means for an individual participant. 

Could you tell me my actual antibody level (rather than positive or negative) and how this compares to other participants in the CLARITY IBD cohort?

We are currently discussing this. However, it is important to note that the precise antibody level which correlates with protection against SARS-CoV-2 infection, symptomatic disease and severe COVID-19 are not known

Patients Q & A's around vaccinations.: FAQ

Should patients on Vedolizumab receive a 3rd primary vaccine dose?

Data from the CLARITY IBD study suggests that Vedolizumab does not have a major impact on antibody responses to COVID-19 vaccine. However, in line with the British Society of Gastroenterology guidelines, we recommend vedolizumab-treated patients are offered a 3rd dose. Your local IBD team will be identifying patients who are eligible and sharing this information with GP surgeries and local vaccination centres.

Are participants able to add the dates of a 3rd primary dose, a booster dose or a COVID-19 infection?

Yes. These data will be collected in the 8-weekly questionnaires. In addition personalised links will be provided We are going to be adding further questions to the questionnaire around 3rd primary dose/boosters and also sending out a link to capture this information.

Patients Q & A's around vaccinations.: FAQ
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