Advice from the Joint Committee on Vaccination and Immunisation (JCVI) says people aged over 12 who were severely immunosuppressed when they received a COVID-19 jab - including those with leukaemia, advanced HIV and recent organ transplants - should now receive a third vaccine dose.
The offer of a third dose 'is separate to any potential booster campaign', the JCVI confirmed, and will form part of the primary vaccination schedule for people with immunosuppression.
Patients in this group are being offered a third dose because of evidence that although immunosuppressed people responded to vaccination with an immune response, 'in around 40% of people, the levels of antibodies were low'.
Plans for a wider COVID-19 booster campaign - which interim JCVI advice earlier this year suggested could start from 1 September - remain in doubt.
The JCVI confirmed it is 'still deliberating the potential benefits of booster vaccines for the rest of the population and is awaiting further evidence to inform this decision'.
However, it said that patients with milder immunosuppression - not included in the third dose offer at this stage - are 'likely' to be included in a potential booster campaign.
The JCVI added: 'In the event of a booster programme, it is expected that severely immunosuppressed people will also be offered a booster dose, at a suitable interval after their third dose.'
GP practices were told earlier this year to plan for a COVID-19 booster campaign alongside this year's flu vaccination programme - and guidance from NHS England suggested co-administration of the jabs was likely to be possible.
However, a JCVI expert said last month that only a 'small group' of people may need booster jabs, casting doubt on earlier plans that suggested they could be rolled out to all over-50s, clinically vulnerable patients and those in flu and COVID-19 at-risk groups.
GPs have faced significant challenges planning vaccination programmes amid a lack of detail on plans for boosters - with many now choosing to keep the programmes separate.
Announcing plans for a third dose for immunosuppressed patients, JCVI COVID-19 immunisation chair Professor Wei Shen Lim said: 'We want people with severely suppressed immune systems to have the best chance of gaining protection from COVID-19 via vaccination. Therefore, we are advising they have a third vaccine dose on top of their initial two doses, as we hope this will reduce their risk of severe outcomes such as hospitalisation and death.'
Third vaccine dose
The committee is advising that patients aged over 18 should receive 'either the Moderna or Pfizer-BioNTech COVID-19 vaccines' because of reports that mRNA vaccines have delivered an 'increased immune response in some immunosuppressed people. For those aged 12 to 17, the committee said that 'the Pfizer-BioNTech vaccine is preferred'.
Doctors will be left to decide the timing of third doses, but the JCVI said that 'as a general guide, the third dose should usually be at least eight weeks after the second dose'. This is a flexible timeline to allow doses to be adjusted, for example to allow vaccination before a patient begins chemotherapy.
Those with less serious immunosuppression are not included in this advice but are likely to become eligible for another dose as part of a potential booster programme, pending further advice from the JCVI.
Health and social care secretary Sajid Javid said: 'Today I have accepted the expert recommendations from the independent JCVI to offer a third vaccine dose to people aged 12 and over with severely weakened immune systems.
'The NHS will contact people as soon as possible to discuss their needs and arrange an appointment for a third dose where clinically appropriate. This is not the start of the booster programme - we are continuing to plan for this to begin in September to ensure the protection people have built from vaccines is maintained over time and ahead of the winter.
'We will prioritise those most at risk to COVID-19, including those who are eligible for a third primary vaccine, for boosters based on the final advice of the JCVI.'