No serious adverse events found with next-generation smallpox vaccine

Interim data from a phase I/II clinical trial of a next-generation vaccine for smallpox suggest that the vaccine may provide immunity and thus far the trial has been without any serious adverse events.

Researchers reported their data at the 2005 American Society for Microbiology Biodefense Research Meeting.

LC16m8 is a live attenuated smallpox vaccine that is produced in cell culture from vaccinia virus that has been attenuated, or modified, so that it can initiate an immune response without causing serious adverse effects. Derived from the Lister strain of vaccinia, LC16m8 has been licensed in Japan since 1980 and forms the basis of that country's national vaccine stockpile.

"The preliminary study results are consistent with the far larger Japanese experience," said Dr. Richard Greenberg of the Kentucky School of Medicine, and one of the researchers on the study. "LC16m8, an attenuated smallpox vaccine, has had a 100% take rate and has been well tolerated. Intensive monitoring for myopericarditis has not uncovered any cardiac toxicity in the first 66 volunteers."

"Take rate", or the percentage of vaccinees who form a pock at the site of injection, is a traditional measure of a smallpox vaccine's effectiveness in producing an immune response.

Currently, the only smallpox vaccine that has been licensed for use in the United States, Dryvax®, is made from unattenuated vaccinia virus, a relative of the smallpox virus. Serious side effects have been associated with this and other unattenuated smallpox vaccines, including potentially fatal encephalitis and heart inflammation.

The clinical trial represents the first clinical study of LC16m8 in the United States and is another step forward for VaxGen, Inc. towards its goal of introducing a safer, more effective smallpox vaccine to the United States. The interim data represent the pooled, blinded findings from the first 66 volunteers in the clinical trial.