About 37 million people have now had booster Covid vaccine doses across the UK - more than 64% of those eligible.
The government is urging everyone who can, to come forward and receive the jab.
Is the Covid vaccine compulsory?
For most people in the UK, the Covid vaccine is not mandatory.
Care home staff in England must also already be vaccinated (unless exempt).
Meanwhile a number of employers, including Morrisons, Next, Ikea, Ocado and Wessex Water have cut sick pay for unvaccinated workers who are forced to isolate after being exposed to Covid.
Employees will receive only the statutory-sick-pay (SSP) minimum (£96.35 per week), unless there are mitigating circumstances.
All staff who test positive for the virus will still receive full sick pay, regardless of their vaccination status.
Across the UK, Covid passports providing vaccination status or negative test results are required to enter some venues.
Many foreign countries are restricting entry to vaccinated travellers or imposing restrictions on those who are not.
When can I have a booster?
In Scotland boosters can be booked online.
In Wales people should wait to be invited, with older and higher-risk people being prioritised.
In Northern Ireland people aged 18 to 29 can go to walk-in hubs, and make booster appointments.
Why do I need a booster?
Early studies from UK researchers suggested a booster vaccine - on top of the first two jabs - provides 80-85% protection against Omicron (compared with 97% against Delta).
More antibodies are developed thanks to the booster, giving the body stronger defences against the virus.
It makes it harder for Omicron to infect the body, although current vaccines are still not a perfect match.
Pfizer has started clinical trials of a new Covid vaccine which targets the Omicron variant.
Moderna will soon begin trials of its own Omicron-specific jab, and AstraZeneca has also started working on a new version of its vaccine.
Which children are being vaccinated?
All children aged 12 and over are being offered two doses of the Pfizer jab. They can usually have a second dose 12 weeks after the first.
A low-dose version of the Pfizer vaccine has been approved for children aged five to 11 who have health conditions putting them at greater risk from catching Covid. Eligible children in this age group are now being invited for vaccination in Scotland
Primary school children who live with clinically vulnerable adults should also be offered a jab, government vaccine advisers said.
The Joint Committee on Vaccination and Immunisation (JCVI) also recommended that the normal booster dose should be offered to children aged 12-15 if they:
- are in an at-risk group or live with someone who is immunosuppressed
- have a severely weakened immune system - they should get four doses
It is not yet clear when children will get these doses.
They can make an appointment or attend a drop-in clinic, as can eligible children of the same age in Scotland.
Children who are not considered to be at high risk from Covid should wait 12 weeks after a positive Covid test before having the vaccine.
What vaccine will I get for my booster?
Your booster will be a single dose of either Pfizer or Moderna - regardless of which vaccine you received before.
If you have recently tested positive for Covid, you should wait four weeks from the date of the test before having your booster.
The vaccines do not infect you with Covid, and cannot cause positive results on a lateral flow or PCR test.
What if I haven't had my first or second vaccine?
You can still book your first or second jab. You need to wait eight weeks between the first and second.
In particular, the government wants unvaccinated pregnant women to come forward.
- In England, bookings for over-12s can be made online, by calling 119, or visiting a walk-in clinic
- In Scotland, over-16s can register for their first or second vaccine online, or by calling 0800 030 8013
- In Wales, adults can contact their local health board
- In Northern Ireland, you can book online or call 0300 200 7813; walk-in centres are open to older teenagers
What about side effects?
They are part of the body's normal immune response to vaccines and tend to resolve within a day or two.
There are extremely rare, but occasionally fatal, cases of people developing blood clots after taking the AstraZeneca vaccine.
And a very small number of people have experienced a severe allergic reaction after the Pfizer vaccine.
You should discuss any existing serious allergies with your healthcare professional before being vaccinated.