A man in San Diego was infected with the vaccinia virus — the virus in the smallpox vaccine — in June, 2012 after having sexual contact with someone who'd recently been vaccinated, according to a new report from the Centers for Disease Control and Prevention.
What's more, the infected man also passed the virus along to another unvaccinated individual during sexual activity, a phenomenon known as tertiary transmission, the report said.
The smallpox vaccine contains the live vaccinia virus, which is similar to smallpox but doesn't actually cause the disease. In 1972, the United States stopped vaccinating members of the public against smallpox because the disease had been eradicated. However, in 2002, the Department of Defense resumed smallpox vaccination for its military personnel and civilian employees.
Because the vaccine contains a live virus, it can cause symptoms in vaccinated people, and the virus can spread to others. People can become infected with the vaccinia virus if they touch the vaccination site on a person who has been vaccinated, or if they come into contact with clothing that has been contaminated with the virus. Symptoms of a vaccinia virus infection include a rash, a fever, and head and body aches, according to the CDC.
Since 2002, there have been 115 reports of vaccinia virus transmission between vaccinated and unvaccinated people, according to a review published in 2011. Most transmissions occur through intimate contact, such as sexual relations, or contact between a mother and child. There have also been reports of transmission at gyms