Third doses for people with weakened immune systems

People with a weakened immune system are being offered a 3rd dose of a coronavirus (COVID-19) vaccine. This is also known as a 3rd primary dose.

If you had a weakened immune system when you had your first 2 doses, the vaccine may not have given you as much protection as it can for people who do not have a weakened immune system.

A 3rd dose may help give you better protection.



The 3rd vaccine dose for people with a weakened immune system is different to a booster vaccine dose.

Who can get a 3rd dose of a COVID-19 vaccine

A 3rd dose of a COVID-19 vaccine is being offered to people aged 12 and over who had a weakened immune system when they had their first 2 doses.

This includes people who had or have:

  • a blood cancer (such as leukaemia or lymphoma)
  • a weakened immune system due to a treatment (such as steroid medicine, biological therapy, chemotherapy or radiotherapy)
  • an organ or bone marrow transplant
  • a condition that means you have a very high risk of getting infections
  • a condition or treatment your specialist advises makes you eligible for a 3rd dose

If your immunosuppression started at least two weeks after your second dose of vaccination, it is unlikely you will need a third dose at this stage, but please discuss this with your specialist.

How and when to get your 3rd dose of a COVID-19 vaccine

If you’re eligible, your GP or specialist should contact you to let you know you can get a 3rd vaccine dose.

You may also get a letter from the NHS advising that you may be eligible and to discuss this with your doctor.

You’ll usually be offered a 3rd dose at least 8 weeks after you had your 2nd dose.

Your doctor may suggest a different time depending on if you have any ongoing or planned treatment that affects your immune system.

Your doctor will discuss with you how you can get your vaccine. You’ll usually get vaccinated at your local hospital or a local NHS service such as your GP surgery.

If you think you’re eligible for a 3rd dose but have not been contacted, speak to your doctor.

A third primary dose improves the immune response in people with weakened immune systems who may not have responded well to first two doses.

A booster dose makes the immune response to vaccination last as long as possible in people who are likely to have responded to their first two doses.

The primary course creates the immune response, the booster dose prolongs it.

The third dose should be given ideally at least 8 weeks after the second dose, but the timing will depend on any treatment you may be having. Your specialist will advise on the best time to have your third dose in discussion with you.

Eligible patients should have been contacted by the NHS, letting you know where to book your third dose. If you think you are eligible, but have not yet been contacted, please speak to your GP or specialist.  If your care is currently under a consultant in a hospital, it is possible that they may arrange it for you. 

If you’re aged 18 or over and have a letter from a GP or hospital consultant confirming you’re eligible for a third dose, you can also go to a walk-in vaccination site.

If you are offered a booster appointment before your third dose, and your GP or specialist are happy with the appointment timing, you could book the appointment, but you must make it clear to the vaccination team before your injection that you require a third dose rather than a booster. This is to ensure you get the correct vaccine at the correct dose. It might help to take with you documentation confirming your health condition and treatment plan.

Most people will be offered a third dose of the Pfizer/BioNTech vaccine or Moderna vaccine.
This means your third dose may be different from the vaccines you had for your first and second doses.

Some people may be offered a third dose of the Oxford/AstraZeneca vaccine; this will be decided with your specialist.

It is likely that you will require a booster vaccine (fourth dose) approximately six months after your third vaccine dose. However, evidence from clinical trials about this is still under review, so the optimal timing is yet to be confirmed. 

If you are about to receive immunosuppressive treatment, your booster may be given a minimum of four months (120 days) after your last dose to avoid giving the booster when the immune system is less able to respond. Please speak to your GP or consultant about this.