February 6, 2004

VUMC study: Smallpox vaccine poses low risk

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Dr. Thomas Talbot

VUMC study: Smallpox vaccine poses low risk

Results of the most comprehensive U.S. smallpox study to date —conducted at Vanderbilt University Medical Center — prove that people inoculated with the smallpox vaccine pose a low risk of infecting others if proper bandaging and hand-washing techniques are followed.

Study results, published in the Feb. 15 issue of Clinical Infectious Diseases, may put to rest concerns over the risk of health care workers, or others such as military or emergency workers, vaccinated for smallpox of passing the disease along to at-risk members of the population such as children, pregnant women, and people with immune disorders or certain skin conditions.

“Hopefully, this study has helped reassure individuals about the transmission of smallpox,” said Dr. Thomas Talbot, assistant professor of Infectious Diseases and the study’s lead investigator. “The risk of transmission is vastly reduced if those vaccinated against smallpox keep the vaccine site bandaged and practice good, thorough hand-washing with soap and water, or an alcohol-based product, after changing the bandage.”

About eight or nine days after receiving a smallpox vaccine individuals develop an open wound that sheds live vaccinia virus, (the actual virus used in the vaccine) for several days. The potential risk of spreading vaccinia virus to patients, particularly to those in an at-risk group, led many U.S. healthcare workers to choose not to participate in President Bush’s national smallpox vaccination campaign.

Children, pregnant women, people with eczema or other exfoliative skin disorders, and those with immune disorders can be at serious risk if exposed to the vaccinia virus.

For VUMC’s study, 148 individuals were vaccinated with the vaccinia vaccine. All were vaccine “naive,” having never before received the vaccine. Each participant went through an average of 9.6 bandage changes during the study, and 2,843 cultures were obtained from vaccine sites, outside of vaccination site bandages, and participant’s hands for laboratory analysis. Vaccinia was recovered from only 0.65 percent of the bandage specimens (6 of 918) and from only 0.22 percent of the hand specimens (2 of 926). An extremely low frequency of recovery of the live vaccinia virus outside of the protective bandage. There was also no evidence of transmission of vaccinia to volunteers during the study.

Talbot says he sees no need for everyone to be vaccinated against smallpox. Thanks to civilian and military vaccination campaigns there now exists a backstop of individuals who could step in during a bioterrorism crisis.

“If someone were to intentionally release smallpox, we have our first wave of healthcare responders protected,” he said. “The vaccine can be effectively administered for as long as three or four days after exposure, so healthcare workers who have been vaccinated could take care of patients and help vaccinate everyone else in the days following an attack.”

Whether hospitals that chose not to participate in the national smallpox vaccination campaign, including VUMC, will reconsider policies regarding vaccinations for healthcare workers based on the study’s outcome remains to be seen.

“It’s been an interesting question, and hopefully now we’ve got a lot of contemporary data to help address questions related to secondary transmission risk,” Talbot said.