Chiron was due to supply nearly half of the 100 million flu vaccine doses required by the United States this year.© Banana Stock

US public health officials warn that there will be a dearth of influenza vaccine on the brink of the winter flu season, after a major producer was suspended from making the jab on Tuesday.

The suspension was imposed by a UK regulatory agency because of concerns that some batches of the vaccine are not sterile and carry some kind of contamination. It means that the company, Chiron, will be unable to release any of the vaccine made in its British facility in Liverpool, which is where it produces jabs for the US market.

Chiron announced in August that some lots of its vaccine might not be sterile, and informed the regulatory authorities. The company says that it then performed careful safety tests, and showed that the problem was confined to a few batches. It says it is confident that the vast majority of the vaccine is safe.

But on 5 October, Britain's Medicines and Healthcare products Regulatory Agency (MHRA) informed Chiron that it had safety concerns about the entire production facility and suspended the firm's licence. Chiron's president and chief executive officer, Howard Pien, called the action "disappointing and unexpected

Lack of jabs

The announcement means a huge vaccine shortfall is probable in the United States, where Chiron was due to supply nearly half of the 100 million doses expected. To a lesser extent, the ban will also affect Britain. "The loss of the Chiron vaccine poses a serious challenge to our vaccine supply for the upcoming flu season," said a statement from the US Department of Health and Human Services.

The department says that health authorities will prioritize remaining stocks of the vaccine to those who most need them, probably health workers, children, the elderly and those with illnesses that make them susceptible to infection. The department is also talking to the only other major flu vaccine manufacturer, the French company Aventis Pasteur, to see if it can make up some of the shortfall.

But experts say it will be difficult to produce a large batch of the vaccine in time to meet demand by the start of the flu season. And in a press conference, Pien said it was unlikely that the company's licence would be reinstated and the vaccine released. "Unless they change their minds, this season is gone and those vials will be destroyed," he said.

Problems in the process

The shortage highlights two problems with the system used to manufacture flu vaccines. One is that the jab is mass-produced in millions of hen eggs: Chiron uses 100,000 a day at the peak of production. These have to be ordered months in advance, which makes it difficult to produce a fresh batch of vaccine at the last minute.

The second issue is that the vaccines are made by only one or two firms. This leaves the supply vulnerable to disruption if, as has happened in this case, one of the producers cannot meet demand. "We need more people making flu vaccine," says John Treanor, who evaluates novel vaccinations at the University of Rochester, New York.

Despite the vaccine shortage, Treanor says it is difficult to predict whether the impending flu season will be particularly severe. The virus kills around 36,000 people in the United States each year, but its spread and damage will depend on whether the available vaccine can be targeted to those most at risk, and whether this year's strains are particularly virulent.

Alarm over vaccine shortages also surfaced this time last year, when it was feared that demand for the jab would outstrip supply in a particularly severe flu season. However, that shortfall was far less serious.

"It's going to generate a lot of confusion and concern," Treanor says. "But we would like to avoid any panic-stricken rushing to the clinic."