Study on Effectiveness of Smallpox Vaccine Over Time

The results may help predict the spread of a smallpox outbreak, since nearly 95% of Americans older than 35 were vaccinated many years ago and may still have strong immunity.

The study will look at the effectiveness of both arms of the body's adaptive response: antibodies and T-cells. Blood samples from study participants are exposed to the vaccinia virus in petri dishes. In people with strong immunity, their antibodies will neutralize the virus, saving healthy cells from becoming infected. If the virus is able to slip past this first line of defense and actually cause an infection, a strong T-cell response is necessary to destroy virus-infected cells before they multiply and spread.

"We know that people who contract yellow fever, polio, or measles gain a lifelong immunity to those diseases. Now we want to see if this is universally true for other viruses, such as vaccinia, the virus used for immunizing against smallpox,” said Mark Slifka, Ph.D., assistant professor of molecular microbiology and immunology in the Oregon Health & Science University School of Medicine (Portland, USA; www.ohsu.edu/som), which is conducting the study. The researchers say the vaccine may prove to provide less protection against disease over time. In other words, people might still get infected, but vaccination may still provide enough protection to lower the risk of death.




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