FDA panel recommends smallpox vaccine approval

Lisa Schnirring

May 18, 2007 (CIDRAP News) A US Food and Drug Administration (FDA) panel yesterday recommended that the agency approve a smallpox vaccine made by British biotechnology company Acambis plc that is currently being stockpiled for the US government.

The panel unanimously voted 11 to 0 that ACAM2000 is both safe and effective, Karen Reilly, an FDA spokesperson, told CIDRAP News in an e-mail after the meeting. The FDA is not bound by the advisory panel recommendations but usually follows them.

Acambis has a contract with the US Department of Health and Human Services (HHS) to make 209 million doses of smallpox vaccine for the Strategic National Stockpile (SNS) to use in the event of a terrorist release of smallpox virus. Marc Wolfson, a spokesman for the HHS Office of Public Health Emergency Preparedness in Washington, told CIDRAP News in an e-mail that the company has delivered 192.5 million doses of ACAM2000 so far and has been paid $573,650,000.

ACAM2000 uses vaccinia virus, a close relative of smallpox, and is grown in cell culture. It is derived from Dryvax, a first-generation vaccine that was used in global smallpox eradication programs. The newer vaccine is grown in cell culture rather than on the skin of calves, which is thought to produce a purer and safer vaccine that has less risk of rare but serious complications.

The positive recommendation came despite some concerns panel members raised about the side effects of the vaccine. Some outside experts who spoke at the meeting said the risk of heart inflammation in people who had been vaccinated warranted further review, according to a Reuters report yesterday.

In 2004 Acambis temporarily halted one of its phase 3 trials comparing ACAM2000 with Dryvax, the currently licensed smallpox vaccine that is no longer produced, after myopericarditis developed in at least three of the research subjects.

Panelists said they had to weigh the risks of heart inflammation, which would be unacceptable for routine vaccination, against the threat that US military personnel and others in high-risk settings face regarding smallpox exposure, Reuters reported.

"This vaccine should not be used lightly," said Pamela McInnes, a panelist who directs the Center for Integrative Biology and Infectious Diseases at the National Institutes of Health.

Panel members said if the FDA approves the vaccine it should require the company to continue clinical trials and other measures, Reuters reported.

Ian Garland, Acambis' chief executive officer, said in a company press release that the FDA panel's recommendation reinforces the company's confidence that ACAM2000 will be licensed. The FDA told Acambis its target date for an approval decision is Aug 31, 2007.

The US Centers for Disease Control and Prevention (CDC) and Acambis are discussing an arrangement for Acambis to provide long-term production of the vaccine using a US-based supply chain and production (ie, warm-base manufacturing), Acambis said in its press release. Having an FDA-licensed product is a prerequisite to finalizing a warm-base manufacturing contract with the CDC, Garland said.

The HHS, in an Apr 20 release of its plan for developing and buying medical countermeasures against a range of biological, chemical, and other threats, said it was planning to stockpile a weaker version of the smallpox vaccinemodified vaccinia Ankara (MVA)for certain groups, such as pregnant women and immuncompromised people, who can't receive the conventional smallpox vaccine. The agency "is well advanced in the pre-award stage" of a program to buy an MVA vaccine. Two companies have developed MVA vaccines: Acambis and Copenhagen-based Bavarian Nordic.