Clubbers and people attending some other venues in England will have to be fully vaccinated by the end of September, the government has said.
From Monday, adults who have had both jabs can avoid quarantine after travelling to amber-list countries - although not France.
How are the rules for nightclubs changing?
Nightclubs in England are only just reopening, following the removal of most Covid restrictions and guidance.
But ministers want "higher risk" settings - including nightclubs - to make use of the NHS Covid Pass, which can prove someone has been fully vaccinated.
At present this is not a legal requirement - so clubs don't have to ask for proof.
Prime Minister Boris Johnson now says he plans "to make full vaccination the condition of entry to nightclubs and other venues where large crowds gather", by the end of September.
By this point, all 18-year-olds in England will have had the chance to be fully vaccinated. The PM said 35% of 18-30 year olds were currently completely unvaccinated.
Sir Patrick Vallance - chief scientific adviser to the government - said nightclubs "are a focus for potential superspreading events" and that has already been the case in the Netherlands and Israel.