Acambis suspends smallpox trials on heart failure fears

Acambis has been forced to halt trials of its flagship smallpox vaccine for the US government after it was linked to an increased risk of heart attacks in some volunteers.

Acambis has been forced to halt trials of its flagship smallpox vaccine for the US government after it was linked to an increased risk of heart attacks in some volunteers.

Shares in the FTSE 250 company, whose fortunes were transformed by an order to supply enough product to inoculate every man, woman and child in the US in the event of a bioterrorist attack, fell 47p to 317p on the news. The share price fall wiped about £50m from the group's market capitalisation.

Safety monitors found five suspected cases of myopericarditis, an inflammation of the heart and surrounding tissue that puts sufferers at risk of heart attacks. To date, trials have involved 2,500 volunteers and Acambis had hoped to vaccinate 2,900 more.

Gordon Cameron, the chief executive, sought to play down the significance of the decision to halt testing. The suspected side effect had been identified both among patients given Acam2000, the company's new smallpox vaccine, and among those given Dryvax, the historic vaccine used to eradicate smallpox that Acam2000 is supposed to supersede.

"We have always known that the smallpox vaccine has potential adverse side effects. That is what has been driving the US government's strategy of not vaccinating their entire population," he said.

The US government has received and paid for most of the smallpox vaccine Acambis is contracted to supply. The company has fulfilled a 155 million dose, $428m contract, and is one-third of the way through supplying a 54 million dose, $110m contract. The payments are not conditional on gaining successful regulatory approval for the product.

Mr Cameron said he did not believe the small number of side effects would derail that regulatory process, and the company may already have enough data to file for approval.

Acambis was given a lump sum from the US government to pay for trials and analysts said that, were they to be halted early, the company could be able to pocket the difference.

However, there were concerns yesterday that the US government may now decide not to replenish Acam2000 stockpiles as they go out of date, preferring to switch its focus to a weaker strain. Acambis is working on such a strain, under the direction of the US authorities, but is in competition with another company for any ultimate orders.

Revelations of potential side effects could also hit sales of smallpox vaccine to other countries, a key plank in Acambis's plan to grow the business. Jonathan Senior, at Evolution Beeson Gregory, said: "...If the product is never approved, some governments will have to rethink their strategy."