Question: I have heard that people with weak immune systems could get very sick, or die, if exposed to people who have received the smallpox vaccine. Is this true?
Answer: The smallpox vaccine is a live virus vaccine called vaccinia. Anyone with a weakened immune system could have a potentially fatal infection from live virus vaccines. In fact, even in people with a normal immune system, there is a risk of death from the smallpox vaccine estimated to be 1-2 deaths/1 million vaccinations. Additionally, the risk of healthy people developing a disseminated vaccinia virus infection, called eczema vaccinatum (EV), a very serious condition, is thought to be about 10-39 people/1 million vaccinations. People with a diagnosis or history of eczema, or atopic dermatitis, are much more likely to develop EV.
According to the Centers for Disease Control (CDC), following vaccination, "a red and itchy bump will develop at the vaccine site in three or four days. In a week, the bump becomes a large blister and fills with pus and begins to drain. During week two, the blister begins to dry up and a scab forms. The scab falls off in the third week, leaving a small scar. People who are being vaccinated for the first time have a stronger reaction than those who are being revaccinated." Live vaccinia virus is present at the vaccination site until the dry scab forms.
There is some risk of transmission of vaccinia virus from a vaccinated person to an unvaccinated person, also referred to as contact vaccinia (CV). John Neff, and colleagues, from Children's Medical Center in Seattle, recently studied this transmission risk, as reported in an article in the Journal of the American Medical Association (JAMA) on October 16, 2002. Most of the reported cases of CV occurred in close household contacts. The risk was found to be about 2-6 cases/100,000 vaccinations. The risk of EV was 1-2 cases/100,000 vaccinations. However, these studies are based on transmission rates observed in the 1950s and 1960s. At that time HIV was not known to exist, not many people were immunosupressed because of organ transplants, not as many people were receiving chemotherapy for cancer, immune-suppressing steroids were used less frequently, and the incidence of eczema in the population was much lower than it is today. These factors would suggest that today there is a much larger pool of people at risk of developing EV if they acquired vaccinia from a person vaccinated. People who have household or intimate contacts who have a weakened immune system, are pregnant, or have any of the above skin conditions should not be vaccinated. This is due to the risk of transmitting vaccinia virus to their close contacts.
What about the risks of a vaccinated health care worker infecting a person with HIV?
In general the reaction to the vaccine is limited to the injection site and with a sterile dressing over that site, and proper hand washing techniques, there probably is little risk of a health care worker transmitting vaccinia to a patient. The Advisory Committee on Immunization Practices (ACIP) October 2002 recommendations stated:
"With respect to administrative leave for health care workers, the ACIP does not believe that health care workers need to be placed on leave because they received a smallpox vaccination. Administrative leave is not required routinely for newly vaccinated healthcare workers unless they are physically unable to work due to systemic signs and symptoms of illness, extensive skin lesions which cannot be adequately covered, or if they do not adhere to the recommended infection control precautions. It is important to realize that the very close contact required for transmission of vaccinia to household contacts is unlikely to occur in the healthcare setting."
In the conclusion of their paper on CV, Neff and colleagues write:
"... any large-scale response, such as the one proposed by the CDC, has the potential to result in more cases of contact vaccinia. An orderly, systematic approach along with careful screening to identify possible vaccinia-susceptible individuals and household contacts and close monitoring for adverse effects are essential to reduce the risk of transmission of vaccinia following smallpox vaccination."
In several presentations that I have heard on the proposed smallpox vaccination programs, officials from both the National Institutes of Health and the CDC have expressed their concern and awareness of the risk of contact transmission of vaccinia to immunocompromised people. I think that a limited, planned smallpox vaccination program can be conducted which will minimize the risk of transmission of vaccinia or contact vaccinia. However, were there to be a small pox attack, and a massive vaccination program initiated, it is unclear if minimizing contact vaccinia could or would be a high priority. The CDC is currently recommending that the smallpox vaccine be given to a person with a weak immune system in the case of an actual face-face contact with a person infected with smallpox. The rationale for this recommendation is that the risk of death from smallpox would be greater than the risk of life-threatening complications from the vaccine.
For more in-depth materials about small pox vaccination see the CDC's Web site at: www.bt.cdc.gov/agent/smallpox/vaccination/index.asp.
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Dr. Jeff Schouten is a former general surgeon who has been living with HIV for over 14 years. He is chair of STEP's Publications Advisory Committee and contributes regularly to the STEP Perspective. He has also earned a law degree from the University of Washington, so HIV-related legal questions, as well as medical, will be accepted.