As expected, a new smallpox vaccine from the UK’s Acambis has been recommended for approval by a US regulatory panel if needed ahead of a bioterrorist threat.

The Vaccines and Related Biological Products Advisory Committee of the US Food and Drug Administration has voted unanimously that Acambis' smallpox vaccine, ACAM2000, is both safe and efficacious in situations where it is determined that there is high risk of exposure to the virus.

In summing up, the FDA acknowledged that "there are serious safety concerns" associated with smallpox vaccines such as Dryvax, an older jab that used to be manufactured by Wyeth and ACAM2000, including rare cases of severe skin infections, myopericarditis – inflammation of the heart and the surrounding sac. However, in clinical trials of Acambis’ vaccine, the agency said there were no fatalities.

The panel said one of the studies involving the vaccines suggested the rate of myopericarditis is higher than previously suspected and is about one in 150. "However, the potential benefits of administration of ACAM2000 during a smallpox outbreak to persons who are determined to be at high risk of exposure or who have been recently exposed outweigh potential risks," it added. Nevertheless, Prof Monica Farley, a panel member, said that "if we were looking at this vaccine for routine use in the general population, this rate of myocarditis would be unacceptable."

Black box warning

If approved, the FDA said ACAM2000 would carry the agency's strictest black box warning similar to the one on the Dryvax label discussing the risk of myocarditis and other safety issues. Acambis has proposed a post-approval study and it would participate in an existing registry run by the US Department of Defense to track cases of myocarditis and myopericarditis.

While smallpox has been eradicated for some 30 years, Gerald Parker of the Health and Human Services Department, told the panel meeting “there is some probability that we may see smallpox in the future, therefore we must be prepared [and] I don't want to be in a position that we don't have a vaccine when we could have.''

If the FDA gives the vaccine final approval, and it nearly always follows the recommendations of its advisory committees,

Acambis will be eligible to take up a five-10-year manufacturing contract from the US Centers for Disease Control and Prevention.

It has already supplied 192.5 million doses of the vaccine to the US government's emergency stockpiles and a long-term manufacturing contract could be signed later this year, which could be worth around $30 million a year to the company.

That deal would go some way to compensating for the loss, to Bavarian Nordic, of a different smallpox contract in November which was valued at $545 million. The FDA will give its final decision before the end of August.