In a statement on 9 September, the MHRA confirmed that COVID-19 vaccines made by Pfizer and AstraZeneca could be used 'as safe and effective booster doses'.
The update from the regulator comes after health and social care secretary Sajid Javid said this week that he was 'confident' a booster campaign would start this month, and that he expected final advice from the Joint Committee on Vaccination and Immunisation (JCVI) 'within days'.
The scope of a potential booster campaign remains unclear, however. Interim advice from the JCVI in June suggested booster jabs could be rolled out to people aged over 70, those who are clinically vulnerable and health and care staff alongside a flu jab from 1 September.
The interim advice suggested the campaign could then widen to cover all people aged over 50, 16- to 59-year-olds in flu or COVID-19 at-risk groups and household contacts of some at-risk patients.
However, later comments from a JCVI member suggested booster jabs may only be necessary for a much smaller group of people.
MHRA chief executive Dr June Raine said: 'We are committed to getting safe and effective COVID-19 vaccines to the UK public. This means ensuring that existing COVID-19 vaccines can continue to be used in the most effective way possible.
'We know that a person’s immunity may decline over time after their first vaccine course. I am pleased to confirm that the COVID-19 vaccines made by Pfizer and AstraZeneca can be used as safe and effective booster doses.
'This is an important regulatory change as it gives further options for the vaccination programme, which has saved thousands of lives so far. It will now be for the JVCI to advise on whether booster jabs will be given and if so, which vaccines should be used.'
The MHRA said its decision to approve use of the vaccines for a booster campaign followed 'a careful review of available data on safety and effectiveness of booster or supplementary vaccine doses by the MHRA and the independent Commission on Human Medicines (CHM).
The JCVI has already backed a third dose of COVID-19 vaccine for patients with severe immunosuppression at the time of their first or second dose. However, the committee was clear this should be considered part of the primary vaccination schedule for people in this group, and was not part of the booster campaign.
The UK's four chief medical officers are also considering whether to back COVID-19 vaccination for children aged 12-15, after the JCVI said benefits 'marginally outweigh' risks for this group, but stopped short of recommending a rollout.