Smallpox Vaccine Contraindicated in High-Risk Populations

Internal Medicine World ReportApril 2005

Smallpox Vaccine Contraindicated in High-Risk Populations

By Rebekah McCallister

With the numbers of immunocompromised persons in the United States continuously increasing and with the increasing threat of bioterrorism, the Joint Task Force on Smallpox Vaccination for Allergists has issued a new report warning physicians that a large segment of the population should not be administered the live-virus smallpox vaccination under nonemergency conditions. Such patients include those taking high-dose corticosteroids, those with atopic dermatitis, and anyone with a compromised immune system, regardless of cause. The report was a combined effort by the American Academy of Asthma, Allergy and Immunology and the American College of Asthma, Allergy, and Immunology (Ann Allergy Asthma Immunol. 2005;94:4-7).

Today’s vaccine smallpox vaccine (Dryvax) contains live vaccinia (not variola) virus, which carries important differences from the original vaccine that wiped out natural smallpox from the planet by 1980, noted Charles J. Hackett, PhD, Daniel Rotrosen, MD, and Marshall Plaut, MD, from the National Institutes of Health in an accompanying editorial (pages 1-3).

They point out that many more Americans are now at risk for acquiring the virus from receiving the vaccine itself or having contact with a vaccine recipient than was the case in 1978, when the vaccine was last widely distributed.

Immunocompromised persons include nearly 1 million patients with HIV/AIDS, >150,000 transplant recipients, who are taking immunosuppressive drugs, and an increasing number of patients with autoimmune diseases who are being treated with immunosuppressive or anti-inflammatory drugs. The vaccine is therefore contraindicated in these populations, as well as in patients with a history of or active eczema or atopic dermatitis.

“Patients with atopic dermatitis are at a greater risk of inadvertently contracting vaccinia infection, resulting in eczema vaccinatum, and also of spreading the virus than are persons with healthy skin. Infection may occur in patients with active or quiescent atopic dermatitis,” states the Joint Task Force. “Since one of the primary immunologic protective mechanisms to the virus is T-cell—mediated immunity, patients with this comprised immune response may be more susceptible to smallpox vaccine complications.”

New vaccines in development may help eradicate some of the complications related to the current vaccine, Drs Hackett, Rotrosen, and Marshall point out. Specifically, a next-generation live vaccinia virus grown in Vero cells under serum-free, sterile conditions have been produced. This differs substantially from Dryvax, which is produced in calf lymph and contains antibiotics and potentially bacteria, they note. Approval for the new vaccine is pending.

In the event of an emergency, such as a bioterrorism attack, these warnings will be viewed in a different light, the report suggests. “In the event of a terrorism attack or exposure, the risk of having serious vaccination complications must be weighted against the risk of experiencing a potentially fatal smallpox vaccination.”

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