The head of the World Health Organisation, Dr Margaret Chan, has cast doubt on the Government's claims that a reliable swine flu vaccine will be available to the public by next month.
Dr Chan said that it would be several months before a safe vaccine was in mass production.
“There’s no vaccine. One should be available soon, in August. But having a vaccine available is not the same as having a vaccine that has been proven safe,” she said in an interview with The Guardian.
“Clinical trial data will not be available for another two to three months.”
Her words appear to undermine assertions made by Andy Burnham, the Health Secretary, that the first vaccines will be ready for use by August, by when it is predicted there could be as many as 100,000 new cases a day in Britain.
Meanwhile, the number of deaths from swine flu in Britain may already be higher than the 16 officially caused by the disease, experts have warned.
Up to one in 200 patients who develop serious swine flu symptoms could die from the disease, they said.
But the official tally of deaths may be an underestimate due to difficulties in assessing causes of death, said the team at Imperial College London.
Prof Azra Ghani said: "For example, we know that flu causes a lot of cases of pneumonia. The cause of death could be recorded just pneumonia and we won't known of it was pneumonia or pneumonia caused by swine flu."
Britain has more confirmed cases of the disease that any other country in Europe and is the fourth worst hit nation in the world.
Nearly 10,000 Britons have been confirmed as suffering from the virus, and 16 deaths are linked to it, including that of six-year-old Chloe Buckley last week.
Dr Oliver Pybus, an evolutionary biologist at Oxford University, said that London will already have developed its own mutated strain of swine flu due to the number of infections.