Covid booster jabs are now being offered to millions more people amid reports of the Omicron variant of coronavirus in the UK, with waiting times between your second and third dose being reduced, too.
In September, the Joint Committee on Vaccination and Immunisation (JCVI) recommended that everyone over 50 be offered a third dose of a Covid vaccine, as well as medical staff and younger adults with medical conditions.
Only those who had had their second jab six months or more ago would be invited for a booster. However, this has now changed in a bid to increase the immunity of UK adults with winter on its way and Omicron UK cases.
Estimates reported elsewhere suggest that 22 million people would be ready for a third vaccine by mid-December. But at the current rate of roll-out, all the most at risk will not be jabbed again until the end of January.
However, millions remain unsure of their eligibility for the jab and how to go about getting it.
Here are some questions about boosters answered.
Why is a Covid booster vaccine needed?
A booster jab will top up the immunity of those already fully inoculated against the virus.
The NHS said a booster jab will help improve the protection you have from your first two doses of the vaccine, helping to give you longer-term protection against getting seriously ill from Covid-19.
Does a booster jab make a big difference to your immunity from coronavirus?
A booster shot of the vaccine developed by Pfizer and BioNTech has a dramatic effect, the firms claimed after a trial.
A booster dose given to patients who had the initial two jabs showed a relative vaccine efficacy of 95.6% when compared with those who did not receive a booster.
Pfizer said that during the study period, there were five cases of Covid-19 in the booster group, and 109 cases in the non-boosted group.
Who is eligible for the booster jab?
Those eligible for boosters now include all UK adults who have had their second dose just three months prior. This still includes people living and working in care homes for the elderly, and frontline health and social care workers.
All those who are clinically extremely vulnerable and anyone aged 16 to 65 in an at-risk group for Covid (who were included in priority groups one to nine during the initial vaccine rollout) will also be eligible for a jab.
Adults who share a household with vulnerable people will also be offered the booster.
At what point do people receive a booster?
Previously, booster doses can only be offered to people who are at least six months on from receiving their second dose of coronavirus vaccine.
However, this waiting time was halved in November, 2021, with adults now only needing to wait for three months after their first dose before getting the booster jab.
What jab will be given as a booster?
The JCVI expressed a preference for people to get the Pfizer jab as a third dose, regardless of which jab they were initially given.
But it said that half doses of the Moderna jab could be used as an alternative.
Some people may be offered a booster dose of the Oxford/AstraZeneca vaccine if they cannot have the Pfizer/BioNTech or Moderna vaccine, the NHS said.
How do I book a booster appointment?
The NHS says most people will be invited to book an appointment at a larger vaccination centre, pharmacy, or local NHS service such as a GP surgery.
People who have not received an invitation can book an appointment online without an invitation.
Can I get the flu jab at the same time as the booster?
Yes. The NHS says that most people who can get a Covid-19 booster vaccine are also eligible for the annual flu vaccine and it is safe to have them at the same time.
The UK's flu season usually begins in September and ends in March but the NHS usually starts to feel the pressure in January.
However Dr McCauley - a prominent flu scientist based at London's Francis Crick Institute - says Brits should prepare for an earlier surge in cases due to a rise in infections overseas.
