Three NHS sites are set to begin a pilot offering to eligible patients, smaller doses of monkeypox vaccine, amid global shortages of the jab.
Clinics in Chelsea and Westminster NHS Trust, Central and North West London NHS Foundation Trust and Locala Health and Wellbeing in Greater Manchester are to begin offering people the lower dose option.
Experts say the reduced shots are just as effective and will mean more people are protected.
The fractional dosing approach has been authorised in the US and the EU, as well as the UK.
More than 3,000 people have been diagnosed with monkeypox in the UK since the epidemic began in May. Most cases of the virus have been among gay and bisexual men.
However, anyone who comes into close contact with someone who has monkeypox could potentially contract the virus. Vaccination can help prevent new cases.
UK officials say more than 33,000 regular dose shots have been given to some of those at the greatest risk of contracting the virus.
But many more, who could benefit from being vaccinated, have not yet been immunised – and stocks of the vaccine are running low.