Skip to main content


0300 111 1234


0300 111 1234


3rd Dose v Booster - What's the difference?

As confusion around the Covid-19 3rd dose and booster continues, your guide to explain which vaccination you should be getting, what the difference is between them, and how to get the one you need.

View and download the guide.

Or read on...


Booster doses are being offered to everyone receiving dialysis treatment and those in chronic kidney disease stage 5 not yet on dialysis (as well as the over 50s, front line healthcare and social care workers and people with some other health conditions). The usual vaccination schedule is two primary doses 8-12 weeks apart, followed by a booster six months after the second dose. 

For these people two doses give a high level of antibodies, and a good chance of high protection from Covid-19. The booster vaccination tops up the antibody level in case it is reducing over time.


There is a special vaccination schedule for patients who are immunocompromised. This is three primary doses, with the third dose given 8 weeks or more after the second dose, and likely to be followed by a booster six months after the third dose (booster to be confirmed).

Third doses are being offered to all kidney and other organ transplant recipients and many patients receiving immunosuppression for kidney disease and other conditions. This is because some immunosuppressed patients don’t get an adequate antibody response after only two doses and need a third dose to give the best chance of high protection from Covid-19. A subsequent booster, probably in Spring 2022, will top up their antibody levels.

(See below for a detailed list of patients who should get the third dose).


Both the booster and third dose are strongly recommended to be an mRNA vaccine (either Pfizer or Moderna), regardless of what the first two doses were, as this has been shown to create a more robust response.  

AstraZeneca should not be used unless there is a good reason why an mRNA vaccine can’t be given, for example due to an allergy. Specialist advice is recommended. 

People having Moderna as their third dose need a FULL DOSE, whereas a half dose is given as a booster.

Flu jabs can be given before, after or at the same time as a third dose or booster.


If you are eligible for a booster or a third dose you should be contacted directly either by your GP, hospital, vaccination clinic or the NHS.

If you are eligible for a booster and it is 6 months since your second vaccination you can book directly on the NHS website.

If you are eligible for a third dose and it is at least 8 weeks since your second dose, try contacting your specialist team or GP. The system varies regionally and there have been delays in contacting patients, leading to some confusion. 

If you eligible for a third dose but are offered a booster, you can have that instead (but not both a third dose and booster this autumn). It is important that this vaccination is either Pfizer or a full dose (not half dose) of Moderna. You will still need a booster 6 months later.


If you continue to have problems getting an appointment for your third dose, you may need to persist. Show your GP or specialist team this guide and refer them to the JCVI advice on third doses for the immunosuppressed. 

Whatever your vaccine status, you should continue wearing a mask, avoid crowded areas as far as possible (particularly indoors or poorly ventilated areas) and try to avoid close contact with others especially if they are known to be unwell. 

If you have not yet been vaccinated, be assured that Covid vaccines are very safe, much safer than catching Covid-19 – this includes pregnant women. Even if you have had Covid, you should have the full schedule of vaccines, for the best protection.

For more detailed information see


Individuals who are immunodeficient including those with: 

  • Blood cancers, including patients with acute and chronic leukaemias, lymphomas, myeloma, Waldenstrom’s macroglobulinaemia.  (For other blood cancers or if you are recovered or recovering from your blood cancer, please check with your specialist.)
  • HIV/AIDS if current CD4 count is <200 cells/µl for adults or children
  • Primary or secondary immune deficiencies

Individuals on treatment that affects the immune system, at the time of or around the first or second vaccination including:

  • Kidney and other organ transplant recipients on immunosuppressants (anti-rejection treatment)  
  • Patients on dialysis after a failed transplant but who are on immunosuppression or have been within the previous 6 months
  • Cancer chemotherapy or radiotherapy in the last 6 months
  • Stem cell transplant in the previous 24 months, or more than 24 months ago but had ongoing immunosuppression or graft versus host disease (GVHD)
  • Prednisolone (oral steroids) 20mg or more a day for more than 10 days in the previous month or 10 mg day or more in the previous 3 months
  • Methotrexate 20 mg or higher per week
  • Azathioprine 3.0mg or greater per kg (of patient weight) per day
  • 6-mercaptopurine 1.5mg or greater per kg (of patient weight) per day
  • Mycophenolate 1g or greater per day in the previous 3 months

(If you are on combinations of these drugs, please check with your hospital specialist.)

Individuals receiving any of the following treatments in the 3 months before their 2nd vaccine:

  • Anti-TNF biologics: infliximab, adalimumab, etanercept, golimumab, certolizumab pegol
  • Other biologics:  tocilizumab, abatacept, ustekinumab, secukinumab, belimumab 
  • JAK inhibitors: baricitinib, tofacitinib, upadacitinib, filgotinib
  • T cell modulators: tacrolimus, ciclosporin, abatacept
  • B-cell targeted therapies including rituximab (in the 6 months before their second vaccine)

This list is by no means comprehensive and other immune therapies will also be included – please check with your specialist.  

Stay up to date with PKD Charity events, patient stories and research news as it happens.


COVID-19, 3rd dose, Booster, Vaccine

  • Hits: 8042