The US government says it is confident that a US-made vaccine, pertussitonis (whooping cough), can protect against the disease that killed thousands of children in the United States in 2014.
The US National Institute of Allergy and Infectious Diseases said it would publish results of a series of tests in December that were conducted after a vaccination programme began in the US and Canada in 2015.
The vaccines used to protect children in those two countries had already been tested, but those tests showed the vaccines did not work in adults.
The results of those tests have not yet been published.
“We think that pertusis vaccine is unlikely to be the cause of deaths in the U.S.,” said the director of the National Institute for Allergy & Infectious Disease (NIAID), Dr Robert W. Thomas.
“It has a very low rate of adverse events, and it is a very robust vaccine.”
The US vaccine programme is one of the world’s most successful, and the first in the world to have been approved for children, and to be used widely by adults.
It was launched in 2015 and the vaccines were licensed in December.
Dr Thomas said the vaccine’s efficacy had been “substantial” and that it had been given to more than 1.8 million people in the two countries.
The test results showed that the vaccine “did not have a significant adverse event profile” in adults, but “we don’t know why it’s not effective in adults”, he said.
He said the results of the tests were preliminary.
Dr W. Patrick McKenzie, a US vaccine specialist at the University of California, San Francisco, said: “We are very confident that the US vaccines are safe and effective for use in the current state of public health in the country.”
He said there were other vaccines being tested to protect against pertussitis, but that “we haven’t had a vaccine that we have tested as thoroughly”.
The vaccine was approved by the US Food and Drug Administration in July and will be sold in the coming months.
The vaccine is made by Merck and licensed by the company.
The first vaccines were made in 1999 in the USA, Canada and Australia, and each country has a separate manufacturer.
A vaccine made by a UK company is now available for use by the British.
Dr McKenzie said the US vaccine “has been the safest in the developed world”.
The NIAID said the tests would provide a “precise estimate” of the efficacy of the vaccine.
“The NIAIDs test is the first to assess the safety and efficacy of a vaccine in a large population and we are confident it will be validated in the UK,” said Dr Thomas.
He added that he was “deeply confident” the vaccine would be effective in the future.
The tests will be conducted at two laboratories, one in the state of Texas, the other in Pennsylvania.
Dr Tom Frieden, the director at the US Centers for Disease Control and Prevention, said the first tests were not yet conclusive.
“What we know from other studies is that the results that are coming out of the UK have been quite reassuring,” he said, adding that the UK was “on track” to complete its first vaccination of children.
He also stressed that the tests had not yet shown that the vaccines worked in adults and said the NIAIDS “will wait and see what the results are before taking any definitive position”.
Dr Thomas, who is also an associate professor of infectious diseases at the Johns Hopkins University School of Public Health, said that the data was not conclusive but that it “wasn’t good”.
He said he was not sure whether the US had done enough testing to find out how effective the vaccine was in the people it was being administered to.
“I would be a little surprised if there wasn’t some improvement,” he told ABC News.
“But I would also be a bit concerned if we weren’t seeing some improvement in the first two months of the next phase of the programme, and that would be the last two months.”