Facts About the Smallpox Vaccine

From the Massachusetts Nurse Newsletter
January/February 2003 Edition

Smallpox vaccine, which is made from a live virus related to the one that causes smallpox, is considered the most dangerous immunization for humans. Before the United States stopped routine smallpox vaccinations in 1972, life-threatening complications occurred at a rate of 15 per million among those who received their first smallpox vaccination, and the number included about one to two deaths.

Vulnerable people include pregnant women, babies younger than a year old and people with HIV or other immune disorders, some types of cancer, organ transplants or histories of skin problems like eczema. No one who lives with a person at high risk should be vaccinated, said Dr. Lisa Rotz, an epidemiologist with the bioterror program at the Centers for Disease Control and Prevention.

Vaccination can also cause problems like soreness and swelling at the inoculation site. In recent trials of the vaccine on healthy young volunteers, about 40 percent to 50 percent had substantial local reactions, 30 percent felt impaired in their daily activities, and about

5 percent took time off from work or studies. 

Dr. William Schaffner, the chairman of preventive medicine at Vanderbilt University, said experts expect that health workers would take more sick time than the research volunteers.

To reduce the chance of transmission, the CDC guidelines call for  the vaccination site be covered with a gauze bandage and tape for two to three weeks, until the scab falls off. Vaccinated health care workers will wear special semipermeable bandages at work, because they are better than gauze at preventing transmission.

Researchers say very close contact is required to spread vaccinia, like touching the vaccination site or an article that has been in contact with it like clothing or a bandage. Infection occurs when the virus enters a break in the skin caused by a cut or a rash.

The Israeli Experience

Israel has successfully vaccinated more than 15,000 soldiers and public health workers against smallpox on a voluntary basis since July with virtually no severe side effects, senior Israeli officials say.

"The United States has much to learn from Israel’s experience," Leonard J. Marcus, the director of the health care negotiation and conflict resolution program at the Harvard School of Public Health, concluded in a recent report on Israel’s medical response to bioterrorist threats.

Though as many as 30 to 50 percent of potential volunteers initially resisted being vaccinated, experts said, volunteer rates rose sharply after public health officials began discussing the program’s risks and benefits, and after medical professionals began being vaccinated.

Dr. Marcus concluded in an October report that after being inoculated, 5 percent of those vaccinated reported side effects like fevers, headaches, muscle pain, fatigue and weakness. Medical literature suggests that one in a million people is likely to die from the smallpox vaccine, and one in roughly 250,000 is likely to suffer serious side effects.

However, Israel uses the Lister vaccine strain, different from the strain used by the United States . Dr. Lev said that Lister was less virulent than the American strain and has fewer side effects. He said Israeli doctors and health professionals had screened out those with health conditions that precluded safe inoculation, like pregnant women and people with ailments that suppress the immune system.

There were only two problematic cases in Israel so far – one a woman with an immune disorder. She was not vaccinated but was infected by her husband, who was. She responded quickly to treatment and recovered fully, Dr. Lev said.