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Some Answers to Smallpox Vaccination Questions

Reports on both U.S. military and civilian vaccination efforts suggest that adverse event rates are low but that clinicians should be alert for cardiac or dermatologic events among vaccinees.

The progress of the U.S. smallpox vaccination effort has been difficult to follow in the media. Now, reports from both military and civilian programs answer many of the questions that physicians and patients might have about this controversial endeavor.

Department of Defense health officials reported that, in less than 6 months, 450,293 military personnel were vaccinated (70% for the first time). Complication rates were similar to those reported in past series; complications included mild generalized vaccinia (36 cases), myopericarditis (37 cases), and 1 case of encephalitis. No vaccination-related fatalities occurred. Ten HIV-infected men were vaccinated inadvertently, with no complications; follow-up continues in 85 pregnant women who were vaccinated inadvertently.

In a separate report on the military vaccination program, authors describe 18 of the vaccine-related myopericarditis cases. All were young men (age range, 21-33) who had not been vaccinated previously. Characteristic symptoms appeared at a mean of 10 days after vaccination, and patients either had recovered or were convalescing at the time of the report. All diagnoses were made by excluding other likely causes of disease.

A smallpox vaccination program in a civilian population revealed an apparently new complication of vaccination: noninfectious folliculitis, which occurred in generalized form in 4 and in focal form in 11 of 148 vaccinees. Although morphologically similar to generalized vaccinia, these lesions showed no evidence of direct viral etiology on biopsy or culture and resolved without scarring.

Researchers also probed responses to vaccine among previously vaccinated people. Revaccination success rates ranged from 95% in those who received undiluted vaccine to 53% in those who received 1:32 dilutions. Neutralizing antibody titers in these subjects before revaccination were similar to those seen in newly vaccinated people, which suggests that B cell memory of vaccination can persist for decades.

Comment: Editorialists call the observation that smallpox vaccine can be administered safely to military personnel "a critically important piece of new information," although they note that complication rates could be higher in older, less carefully screened, civilian populations. We don't know if long-term persistence of neutralizing antibody titers confers complete protection against disease, but the presence of even moderate titers in the previously vaccinated cohort ultimately could be helpful in constructing vaccine policies for older people.

— Abigail Zuger, MD

Published in Journal Watch General Medicine July 11, 2003

Citation(s):

Grabenstein JD and Winkenwerder W Jr. US military smallpox vaccination program experience. JAMA 2003 Jun 25; 289:3278-82.

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• Medline abstract (Free)

Halsell JS et al. Myopericarditis following smallpox vaccination among vaccinia-naive US military personnel. JAMA 2003 Jun 25; 289:3283-9.

• Original article (Subscription may be required)
• Medline abstract (Free)

Talbot TR et al. Focal and generalized folliculitis following smallpox vaccination among vaccinia-naive recipients. JAMA 2003 Jun 25; 289:3290-4.

• Original article (Subscription may be required)
• Medline abstract (Free)

Frey SE et al. Response to smallpox vaccine in persons immunized in the distant past. JAMA 2003 Jun 25; 289:3295-9.

• Original article (Subscription may be required)
• Medline abstract (Free)

Wright ME and Fauci AS. Smallpox immunization in the 21st century: The old and the new. JAMA 2003 Jun 25; 289:3306-8.

• Original article (Subscription may be required)
• Medline abstract (Free)