Smallpox vaccine and people with an impaired immune system
The last case of naturally occurring smallpox was seen in 1977; in 1980, the World Health Organization (WHO) declared the disease eradicated and recommended that all countries cease vaccinating people against the disease. However, in response to the possibility of smallpox being used as a biological weapon, the Centers for Disease Control and Prevention (CDC) has developed recommendations for people who have an impaired immune system.
What risks does smallpox pose to people with an impaired immune system?
The last cases of smallpox disease occurred more than 30 years ago. At that time, little was known about immune system problems. While we know considerably more about the immune system now, we do not know much about the effect of smallpox on people with immune system problems. Experts believe that smallpox infections in these people may be more serious than in people with a healthy immune system.
What risks does the vaccine pose to people with an impaired immune system?
All people who receive smallpox vaccine have some risks from the vaccine. The vaccine is made from a live vaccinia virus (not smallpox virus). People who have immune system problems are often advised to avoid vaccines made from live viruses because their immune systems cannot stop the growth of the virus in their bodies.
The risk of severe reactions from smallpox vaccine in people with immune system problems is not known. There have been a few cases of a serious vaccine infection in people with HIV who have received the smallpox vaccine. This infection spreads through the body and can occur in two forms: generalized vaccinia and progressive vaccinia. In rare cases, these conditions can lead to fatal illnesses. There is no proof that receiving a smallpox vaccination will worsen existing immune system problems.
It is unknown what level of immunosuppression (white blood cell count) would put a person with immune system problems at risk for severe reactions from the vaccine.
Should I get the smallpox vaccine?
In an outbreak, everyone who has been in close contact with a person who has smallpox or who was exposed to the virus is advised to receive the vaccine, regardless of age, allergies, pregnancy, or medical conditions.
If you have been exposed to smallpox virus, the vaccine would be advised for you to try to prevent or lessen the infection.
If you have not been in contact with smallpox virus or a person with smallpox, you should not be vaccinated until you have completed any treatments that affect your immune system. Often, the waiting period can be as long as 3 months after finishing treatment. Your health professional can advise you on when it will be safer to receive the vaccination.
What do I do if I am vaccinated and think that I am having a bad reaction?
Call a health professional right away. Tell him or her what is happening, the date and time that it started, and when the vaccination was given. Your health professional will advise you what to do next.
[Adapted from the CDC's Smallpox Vaccination Clinic Guide1]
Last Updated: January 26, 2009
Author: Bets Davis, MFA