More than four out of five UK adults have now had two jabs, but reported daily Covid cases remain high.
Meanwhile, it's been confirmed that millions of people will get booster vaccines - while children aged 12-15 will be offered single doses.
Why are infections still high when so many are vaccinated?
The vaccines are designed to protect people against becoming seriously ill or dying from Covid-19.
They're less effective at stopping people becoming infected by the virus, developing mild symptoms or passing it on.
Although the vaccine does still reduce the likelihood of these things happening, it might only stop half of infected people from transmitting the virus.
Even if 100% of people in the UK were double vaccinated, the virus would still spread - but the key difference is that far fewer people would become seriously ill.
Do vaccines prevent hospitalisation and death?
They strongly prevent vaccinated people from getting Covid symptoms - and are even better at stopping people from ending up in hospital.
But effectiveness also depends on how well each vaccine works against individual variants. The most common variant in the UK today is Delta.
Public Health England (PHE) studies suggest having two vaccine doses protect 80% of people against getting symptoms from the Delta variant. That's lower than the Alpha variant (89%), because Delta is more infectious. The PHE also found:
- Vaccines are 96% effective at preventing hospitalisation
- Covid deaths in the double-jabbed are four times lower than in the unvaccinated
But there will always be some deaths, particularly in the oldest and most vulnerable, because vaccines aren't perfect.
Having two doses remains the best way to protect yourself. After four or five months, a large study suggests you have the same amount of protection whether you had AstraZeneca or Pfizer. Researchers don't yet have enough data to compare the Moderna jab, but believe it is "almost certainly at least as good as the others".
Some 44 million people in the UK, about 81% of people aged 16 and over, have now had their second jab.
Who will be offered third jabs?
Across the UK, single booster jabs will be offered to:
- Frontline health and social care workers
- Older adults in residential care homes
- People aged 16-49 years old with underlying health conditions which put them at greater risk of severe Covid
- Adults who share a household with vulnerable people
The doses will be offered at least six months after a second vaccination, and are likely to be either Pfizer or Moderna.
England's Deputy Chief Medical Officer, Jonathan Van-Tam, says people should also take a flu jab if it is offered alongside the booster.
Which children will now be offered the vaccine?
All four UK governments have also confirmed healthy over-12s will be offered a single Covid jab.
The UK's chief medical officers argue vaccinating this group will help limit school disruption if Covid spreads during the winter.
There is no vaccine currently approved for use in the under-12s in the UK.
The vaccine is also available for over-12s with underlying health conditions, or those living with others at high risk.
How do I get a vaccine?
In England, adults and those within three months of turning 18 can book a jab online or by calling 119. You can also visit a walk-in clinic without an appointment. All 16 and 17-year-olds are asked to make an appointment through their GP.
In Scotland, over-16s can register to get the vaccine on the NHS inform website or by calling 0800 030 8013. Most health boards also have drop-in vaccination clinics. Over-12s can go to drop-in clinics from Monday 20 September.
In Wales, adults should contact their local health board if they've not been offered their jab.
In Northern Ireland, you can book online or call 0300 200 7813. Walk-in centres are open to older teenagers.
How soon should I get my second jab?
In England, the recommended gap between first and second jabs is between 8-12 weeks.
In Wales, the government says you should be called in for your second dose "within 12 weeks" of the first.
In Scotland and Northern Ireland the recommended gap is eight weeks.
Which vaccine will I get?
People who are under 40 or pregnant are being offered Pfizer or Moderna rather than Oxford-AstraZeneca, because of concerns about a possible connection with extremely rare cases of blood clots.
Under-18s are currently being offered Pfizer, although the Moderna vaccine has also been authorised for use in children in the UK.
Is vaccination compulsory?
It's not compulsory, although the health secretary has said it is "highly likely" that both Covid and flu jabs will be compulsory for all frontline NHS and care workers in England.
Being fully vaccinated will also be a condition of entry for nightclubs and some other events in Scotland from 1 October.
It also means you don't have to self-isolate after visiting amber list countries or if a contact tests positive for Covid (as long as you test negative).
England's chief midwife has also urged pregnant women to get the vaccine.
What about side effects?
The most common ones include a sore arm, headache, chills, fatigue and nausea.
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.
Separately, a very small number of people have experienced a severe allergic reaction after receiving the Pfizer vaccine.
You should discuss any existing serious allergies with your healthcare professional before being vaccinated.