Fourth-dose Covid booster vaccines increase protection against Covid-19, particularly in people aged over 70, according to a UK trial.
But scientists say any short-term protection against infection is likely to fall away quickly.
A larger group of people may be offered a booster in the autumn, but any decision will be based on advice from the UK's vaccine committee.
It is likely to look at whether new worrying variants are spreading, and Covid pressure on hospitals.
Some countries, such as Israel and Germany, have already started offering all adults a fourth dose.
Who is eligible for a fourth dose?
adults aged 75 and over
those aged 12 and over with weakened immune systems
You can book an appointment online three months (91 days) after your previous dose. However, to get maximum protection, the NHS recommends having the spring dose about six months later.