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CDC: Transmission of Vaccinia Virus After Sexual Contact with Recent Vaccinee

The Centers for Disease Control published details this week on an interesting epidemiological case of a man in San Diego being infected with the vaccinia virus — the virus in the smallpox vaccine — after having sexual contact with someone who had recently been vaccinated. 

The vaccinee was identified as a civilian who had received his first smallpox vaccine in
June 2012 under the U.S. Department of Defense (DoD) smallpox vaccination program who reportedly did not keep the site covered as instructed. Because the vaccine contains a live virus, it can cause symptoms in vaccinated people, and the virus can spread to others if they touch the vaccination site, or if they come into contact with clothing that has been contaminated with the virus. 

In a case of tertiary transmission, the infected man also passed the virus along to another unvaccinated individual during sexual activity, the report said. This is the first reported instance of tertiary vaccinia transmission through sexual contact. 

While smallpox vaccinations for the general public stopped several decades ago, the DoD resumed vaccination in 2002 for designated military personnel, civilian employees, and contractors. Since this time, there have been 115 reports of secondary transmission of vaccinia virus from military smallpox vaccinees have been reported among intimate, sports-related, and household contacts. Tertiary transmission has also been reported among household and sports contacts and from mother to child through breastfeeding. 

The smallpox vaccine licensed for use in the United States contains live vaccinia virus. The CDC Laboratory Response Network supports a nonvariola Orthopoxvirus test that can identify vaccinia and other nonvariola orthopoxviruses in clinical specimens. 

The study highlights the potential for the vaccinia virus to spread beyond the immediate contacts of a person who has been vaccinated and underscores the importance of following post-inoculation instructions to keep the vaccination site carefully covered. 

The findings were published this week in the CDC’s Morbidity and Mortality Weekly Report.

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