The monkeypox vaccine rollout has stalled in Brighton after stocks of the jab ran out, the BBC understands.
Local MP Lloyd Russell-Moyle said only those with an existing appointment will be vaccinated until further stocks arrive.
He also raised concerns the rollout could be paused in other areas.
The UK Health Security Agency (UKHSA) has said 100,000 doses are due to arrive in September and urged people to be aware of symptoms.
The latest UKHSA figures show there have been 69 cases of monkeypox in Brighton to date, the highest number of cases outside of London.
After a briefing with the agency, Brighton Kemptown MP Mr Russell-Moyle told the BBC he was told there are only around 5,000 vaccines left in the UK.
Another source, who did not wish to be named, confirmed the details of the briefing.
A spokesperson for the UKHSA was unavailable to comment on whether or not clinics would be pausing vaccinations.
It is understood remaining stocks of the jab will be allocated to local sexual health services in the coming days, but that Brighton will not receive more vaccines until the end of next month.
Mr Russell-Moyle said: "Ive already spoken to people in the area who feel worried, scared and that theyve missed out. They feel that theyre being put at risk, and that their enjoyment of the summer is being put at risk by bad organisation from the government."
Sources have told the BBC that low stocks of the vaccine are also set to impact other parts of the country in the coming days.
It is understood that those who already have an appointment will still receive a vaccine, but that after the current 5,000 remaining vaccines have been allocated to local sexual health clinics, no further jabs will be available until the end of September. It comes after similar claims in Scotland.
Mr Russell-Moyle added: "My understanding is that if you are not vaccinated in the next couple of weeks, then it will be too late and youll have to wait until September".
The latest figures from the UK Health Security Agency show that there have been 2,914 confirmed cases of monkeypox since the start of the year.
According to NHS England figures, more than 25,000 people have so far received a vaccine.
Currently about 75% of monkeypox cases are in London, which is where the majority of vaccines have been targeted, but numbers outside the city are also increasing.
The UK government has bought stocks of smallpox vaccine to guard against monkeypox. Monkeypox is caused by the monkeypox virus, a member of the same family of viruses as smallpox, although it is much less severe and experts say chances of infection are low.
The global outbreak of monkeypox has meant a surge in demand for the vaccine. However, stocks are limited as until recently the disease had not spread widely outside of countries where the virus is endemic.
On Wednesday, Dr Mary Ramsay, Director of Clinical Programmes at UKHSA, told the BBC the agency had moved early to procure over 150,000 doses of the smallpox vaccine from the global manufacturer. Around 50,000 of these have been received to date and made available to the NHS for distribution across the country.
"The remaining approximately 100,000 doses is expected to arrive in the UK in September. The thousands of vaccines administered by the NHS to date among those at highest risk of exposure should have a significant impact on the transmission of the virus," she said.
Countries around the world, including the UK, are suddenly scrabbling to get hold of the vaccine.
It was originally designed for a more deadly disease - smallpox - and only limited stockpiles are kept in case of bio-terrorism.
Every dose now being given to tackle an unprecedented monkeypox outbreak is being manufactured first and there is large demand around the world.
So the idea that everyone at risk could be vaccinated immediately has always been a fantasy. Even the United States, with its huge buying power, has a shortage.
Another 100,000 doses will arrive in the UK late next month.
Until then doses have been distributed around the country and health officials are assessing how long current supplies will last.
Exactly which parts of the UK - or all of it - will run out and for how long is being calculated and should be announced soon.
September feels a long way off if youre at risk of catching monkeypox, but the reassuring news is that the number of new infections is already starting to level off.