Researchers studying the possible health risks that could result from the resumption of smallpox vaccinations for the general public say an increased number of newly vaccinated people will be transmitting the virus to others.
In looking at data on mass smallpox vaccinations in the United States, the United Kingdom and Sweden from 1947 to 1968, researchers at the U.S. Centers for Disease Control and Prevention say such transmissions – known as contact vaccinia – during that period were about two to six cases per 100,000 vaccinations. However, such factors as increased numbers of people with weakened immune systems, a reduced natural immunity in the population since vaccinations ended in 1972, and higher rates of the skin condition eczema – a condition linked to contact vaccinia – make more transmissions likely (JAMA, 2002; 288; 1901-05).