103 women had smallpox shots during or before pregnancy, CDC says

May 2, 2003 (CIDRAP News) – A total of 103 women in recent months inadvertently received smallpox shots while pregnant or just before becoming pregnant, despite screening to prevent that scenario, the Centers for Disease Control and Prevention (CDC) reported yesterday.

The agency said the screening appears to be effective, but it plans to investigate the situation anyway.

Eighty-five of the 103 women were among 52,185 women vaccinated in the military smallpox immunization program, the CDC reported in Morbidity and Mortality Weekly Report. Six women were among 6,174 women vaccinated in the program for civilian health workers, and the other 12 women were participants in clinical trials of smallpox vaccines. The total number of women who were vaccinated in those studies was not available.

Smallpox vaccination is not recommended for women who are pregnant or may conceive within 4 weeks because of the risk of fetal vaccinia, a rare but serious condition that often results in fetal or neonatal death or premature birth, the report notes. It says about 50 cases of fetal vaccinia have ever been reported worldwide, including three in the United States.

Of the 85 women immunized in the military program, 62 conceived before vaccination and 23 conceived in the 4 weeks afterward, the report says. Of the six civilian health workers, 2 women are believed to have conceived in the week before vaccination, and four conceived in the 4 weeks following. Two of the women had early miscarriages, the CDC says. The report does not mention any pregnancy-related problems in any of the other women.

The CDC recommends that any woman concerned that she might be pregnant should take a pregnancy test the day she plans to be vaccinated. However, pregnancy tests can miss very early pregnancies, the report notes. Pregnancy testing would not have prevented vaccination of any of the six women in the civilian health worker program, since they had just conceived or were not yet pregnant, the article says.

Despite the vaccinations of pregnant women, screening and education efforts "appear to be effective in deterring women who are pregnant and might not know it from receiving smallpox vaccine and in preventing pregnancy during the 4 weeks after smallpox vaccination," according to the CDC.

The rate of inadvertent vaccination of pregnant women in the civilian and military programs so far is about 1 in 1,000 women of reproductive age, the CDC calculates. Given the general population rate of unknown pregnancy and rate of conception during a 4-week period, the CDC estimates that 12 out of 1,000 reproductive-aged women would be exposed to the vaccine during pregnancy in the absence of screening and counseling.

Nonetheless, the vaccinations of pregnant women have promoted the military services to revise their education materials and expand the questions about pregnancy on screening forms, the report says. CDC is reviewing its recommendations for pregnancy screening and education in the civilian program. In addition, both the CDC and the Pentagon are investigating to determine why pregnant women were exposed to the vaccine.

Aside from fetal vaccinia, smallpox vaccine has not been shown to cause serious birth defects or other problems in fetuses or neonates, according to the report.

CDC. Women with smallpox vaccine exposure during pregnancy reported to the National Smallpox Vaccine in Pregnancy Registry—United States, 2003. MMWR 2003;52(17):386-8

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