Study to test effects of smallpox vaccine in previously vaccinated people

Apr 5, 2002 (CIDRAP News) In the wake of findings that diluted smallpox vaccine remains effective, researchers at Saint Louis University (SLU) are launching a new study on the effects of diluted and full-strength smallpox vaccine in adults who were vaccinated against the disease in childhood.

Investigators at SLU began vaccinating volunteers for the new study this week, according to Joe Muehlenkamp, an SLU media spokesman. The study is sponsored by the National Institute for Allergy and Infectious Diseases (NIAID) and is being led by Sharon S. Frey, MD, first author of the previous dilution study

The researchers are seeking 90 volunteers for the study, Muehlenkamp said. The participants will be divided into two groups: people between 32 and 60 years old who were vaccinated for smallpox as children, and people between 18 and 32 years old who were never vaccinated. The previously inoculated people will receive either full-strength vaccine or vaccine diluted by a ratio of 3.2:1, 10:1, or 32:1, according to an SLU news release. All the unvaccinated volunteers will receive full-strength vaccine.

"Study participants will be healthy adults who don't have eczema or problems with their immune system," the news release states. "They should not have household or direct contact with anyone who is pregnant, has eczema or has any weakness in his or her immune system."

SLU was the site of a small NIAID pilot study on the effectivenesss of diluted smallpox vaccine. That study was used to design a larger trial of diluted vaccine, conducted at SLU and three other sites late in 2001. As reported last week, vaccine used in the larger study still elicited an immune response when diluted five-fold and ten-fold, suggesting that the nation's current stockpile of 15.4 million doses can be stretched to at least 77 million doses. The findings were published online by the New England Journal of Medicine last week.

In the main dilution study, 15 volunteers had no response to a single vaccination, and six of these had preexisting antibodies, suggesting that they had been vaccinated in infancy, according to the NEJM report. "Whether or not persons vaccinated more than 30 years previously can be successfully revaccinated with diluted vaccine . . . remains to be determined," the report states.