DENVER—The live-virus smallpox vaccine has one of the highest rates of serious adverse events of all vaccines. People with a history of atopic dermatitis (AD) are at risk of developing potentially life-threatening eczema vaccinatum (EV) from either vaccination or exposure to someone who has been vaccinated.

A recent review pointed out that the risk for serious complications may be much greater today than 30 years ago, when the smallpox vaccine was last used.[1] Adverse events are most common in patients immunized for the first time. Currently, it is estimated that about 40% of the population of the United States has never been exposed to the vaccine and is at risk for side effects.

According to principal author Donald Y. M. Leung, MD, PhD, Head of Pediatric Allergy-Immunology at the National Jewish Medical and Research Center in Denver, another reason the risk of adverse events is greater now is “because there is a higher prevalence of individuals with an impaired immune response—ie, more people with AD, HIV infection, and patients on immunosuppressive drugs for cancer or transplants.”

THE AD CONNECTION

In 1964, a study of a mass vaccination campaign in England and Wales followed 6.5 million people, about half of whom had received the vaccine for the first time. One hundred eighty-five developed EV and 11 died.[1]

Of those with EV, 80% had a history of atopic eczema, 4% had seborrheic eczema, and 16% were not definitely classified. Two thirds of patients with atopic eczema did not have active disease at the time of vaccine exposure. Accidental primary vaccination (contact with another person who had received the vaccine) accounted for 65% of EV cases.

The prevalence of AD has increased markedly in the last half-century. In the United States, the lifetime prevalence of AD is currently at least 10% to 15%. It is therefore likely that this many people have a history of eczema. According to Dr. Leung, if each person with active or quiescent AD had two close contacts, then up to half the American population would not be eligible for routine immunization with the smallpox vaccine.[1]

Dr. Leung added that other atopic conditions, such as asthma and hay fever, warrant a closer look. “Although patients with … asthma and hay fever are not known to be at risk for EV, keep in mind that up to 80% of patients with [AD] go on to have asthma and hay fever,” he said. “Such individuals are still at risk for EV even after outgrowing AD and must be screened for a history of itchy skin rashes.” Patients with such a history should not receive the smallpox vaccine.

THE NEAR FUTURE

In the event of a widespread smallpox vaccination program, physicians will have to be able to accurately screen people for AD. Dr. Leung said that a protocol for identifying people with AD is being developed by the CDC and should be released within the next few months.

For someone with AD who inadvertently receives the vaccine, said Dr. Leung, “vaccinia immune globulin will reduce the adverse effects, but there currently are only 700 doses available.” He added that the number of vaccinia immune globulin doses would probably increase significantly during the next year.

—Gale Jurasek