Labour and the Liberal Democrats have pledged to roll out access to the HIV-prevention drug PrEP in England to anyone who needs it.
Currently, access is limited to those taking part in an NHS trial – there is no cap in Scotland, Wales or Northern Ireland.
The Conservatives said thousands of places were still available on the trial.
HIV experts and charities welcomed any plans to widen access to the drug.
PrEP is taken by people who are HIV-negative, but at high risk of infection.
Studies have shown it is almost 100% effective, if taken correctly.
Speaking ahead of World Aids Day on 1 December, Sharon Hodgson, Labour's spokeswoman for public health, said: "No-one should be turned away from this revolutionary drug in the fight against HIV."
The Liberal Democrats have also pledged that anyone who needs PrEP in England should be able to get it for free.
Health Secretary Matt Hancock said: "We are committed to delivering our plan of eradicating HIV transmission in England by 2030.
"In England, we have expanded access to the drug PrEP so everyone who needs it can have access, with thousands more places remaining available on the trial."
The debate over PrEP access in England has centred around responsibility for funding.
NHS England lost a High Court case in 2016 where it had argued that local authorities – who oversee public health budgets – were responsible for preventive services, including PrEP.
Later that year, it set up the PrEP Impact Trial, which, so far, has given the drug to 15,700 people.
However, there have been reports of people struggling to gain a place on the trial – and sexual health experts say they are aware of cases where men have been diagnosed with HIV while they waited.
The trial is currently set to end in late 2020.
Mark Lewis, of the Terrence Higgins Trust, welcomed election commitments on access: "PrEP is a game-changer in preventing new HIV transmissions and yet it remains the missing piece of our prevention tool kit in England.
"In parts of the country, PrEP trial sites have closed to gay and bisexual men due to being oversubscribed. This is putting these men at increased risk of HIV and is simply unsustainable.
"After the election we need to see immediate progress."
Dr Tristan Barber, chairman of the British Association of Sexual Health's HIV special interest group, said it also made financial sense to fund PrEP.
"The cost of treating HIV over a lifetime is about £250,000. The cost of PrEP, a generic drug, is approximately £16 per month."
Dr Barber, who works as a London-based HIV and sexual health Read More – Source