A jab that protects against a virus that causes cervical cancer should also be given to boys, an advisory committee has recommended.
The HPV vaccine is routinely offered to girls aged 12 to 13 at secondary school and is free up until they turn 18.
Now the Joint Committee on Vaccination and Immunisation has advised extending immunisation to adolescent boys at the same age as girls.
The Scottish and Welsh governments have now said they will vaccinate boys.
The Department of Health and Social Care in England said it would carefully consider the JCVI's advice and provide an update on its decision shortly.
Other health bodies welcomed the committee's recommendation, adding that boys had been insufficiently protected against HPV for "too long".
HPV is the name given to a large group of viruses, which can be caught through any kind of sexual contact with another person who already has it.
Doctors say most HPV infections go away by themselves, but sometimes infections can lead to a variety of serious problems.
For boys, this includes cancer of the anus, penis, mouth and throat.
The vaccine has been offered to girls since 2008 as part of the NHS childhood vaccination programme, with boys being said to benefit through herd protection.
But there is still a risk of infection in those who go on to have sex with other men or women who have not been vaccinated.
Campaigners have long since argued that offering the vaccine to boys would further reduce the risk of HPV infection, pointing to successful programmes in other countries.
In July last year, the JCVI was criticised after it said in an interim statement that it could not recommend extension of the national HPV programme.
However, the committee's new report says a combined vaccination programme is "highly likely to be cost-effective".
Responding to the report, the Scottish and Welsh governments announced they would introduce an HPV vaccination programme for boys "as soon as practicable".
The Scottish government added that the age ranges of those to be vaccinated were still under consideration.
Public health bodies welcomed the JCVI's report.
The Royal Society for Public Health said it was "a victory for the public's health".
Its chief executive, Shirley Cramer, said: "Boys have been left insufficiently protected against HPV for too long and it is good news that the UK is following in the footsteps of the other 20 countries already vaccinating boys against HPV."
Prof Helen Stokes-Lampard, chair of The Royal College of GPs, also welcomed it, adding: "We hope parents will take up this important opportunity to get their sons and daughters vaccinated as soon as it is available to them."
The campaign group HPV Action called for the Department of Health and Social Care to accept the JCVI's findings and include boys in a vaccination programme "without further delay".