Scientists work on new smallpox vaccine

Smallpox, eradicated more than 30 years ago, is posing new challenges for federal regulators working to spur development of safer vaccines in case the deadly virus returns.

The Food and Drug Administration and the National Institute of Allergy and Infectious Diseases are seeking ways to use animal tests to determine whether emerging treatments work as well in humans as Sanofi's ACAM2000 vaccine, with fewer side effects.

The agencies discussed potential test methods Friday at a public workshop in Gaithersburg, Md.

Smallpox killed about 2 million people worldwide in 1967, said Bernard Moss, chief of NIAID's laboratory of viral diseases. The World Health Organization began an intensified vaccination program that year and declared the disease eradicated in 1980.

While government laboratories in the United States and Russia hold the only known samples of the virus, federal agencies stockpile smallpox drugs amid concerns about bioterrorism.

"Proving that a drug or a vaccine is effective for a disease that doesn't exist and, more importantly, is unethical to create in a human setting, is a scientific challenge for traditional regulatory science," said Eric Rose, chief executive of Siga Technologies Inc.

"Reasonable judgments" can be made about new countermeasures because scientists have experience using animal models in infectious diseases, said Rose, whose New York-based company won a five-year government contract in May, valued at as much as $2.8 billion, to stockpile 2 million courses of its experimental smallpox antiviral drug.

Smallpox, caused by the 3,000-year-old variola virus, occurs only in humans and has a 30 percent mortality rate. New vaccines are tested in animals infected with related viruses, such as monkeypox, said Sharon Frey, professor of infectious diseases at St. Louis University School of Medicine and a principal investigator on an experimental smallpox vaccine developed by Bavarian Nordic, a Danish drugmaker.

"One of the problems is there is no smallpox, so it's hard to do an efficacy trial against a disease that doesn't exist," Frey said in an interview.