Pregnant pause: Vaccinia given despite screening
CDC forms registry to track women, babies
More than 100 pregnant women have been exposed inadvertently to smallpox vaccine since immunization programs began in U.S. hospitals, the military, and clinical trials, the Centers for Disease Control and Prevention (CDC) reports.
Women who are pregnant or who are planning to become so in the near future were warned not to be vaccinated for smallpox. While a public health investigation continues, the prevailing theory is that most of the women were in a window period in which they were pregnant but would not test positive on screening.
"There is a time period of about two weeks between the conception of an embryo and the implantation of the embryo in the uterus when the pregnancy test would not be positive," says Joe Mulinare, MD, medical epidemiologist in the smallpox activity branch at CDC. "We estimate that eight to 12 women per thousand — [even] if they had a pregnancy test during that period — would not know that they were pregnant."
Still there are indications the screening process worked for the most part. The rate of inadvertent exposure to smallpox vaccine among pregnant women vaccinated during the first stage of the civilian and military programs is approximately one per 1,000.1 That rate is substantially lower than the aforementioned rate of eight to 12 per 1,000.
"In effect, what we found was about one in a thousand women vaccinated inadvertently found that they were pregnant," he says. "So in a way, we could say that we did a lot better then we would have expected. The educational programs that were being used actually didn’t do a bad job. [But] we want to make sure we are doing the best job possible. We want to determine if there are any unique qualities or characteristics of [these] women."
The CDC is working with state health departments and the U.S. Food and Drug Administration to determine how the women received the smallpox vaccine while they were pregnant or just before they became pregnant.
The CDC also has established the National Smallpox Vaccine in Pregnancy Registry. The registry will follow women during their pregnancies and their babies, after they are born, to better understand what happens to pregnant women and their babies who have been exposed to smallpox vaccine. The principal risk factor is fetal vaccinia, a rare but serious infection of the fetus.
The registry includes women found to be pregnant when vaccinated, those who became pregnant within 28 days of vaccination, and those who, while pregnant, were in close contact with a person vaccinated within 28 days. Women reported to the registry will be monitored frequently during each trimester and at the conclusion of the pregnancy to document pregnancy outcomes. Outcomes will be tabulated by trimester and reported.
The CDC recommends that all pre-event smallpox vaccination programs include pregnancy screening and education components with these elements: questioning about the possibility of pregnancy before vaccination and excluding those at risk; asking about the date of the last menstrual period; providing education about fetal vaccinia; counseling women to avoid becoming pregnant during the month after vaccination; recommending abstinence or highly effective contraception; and advising women who believe they might be pregnant to perform a first morning urine pregnancy test on the vaccination day.2
"But [testing] wasn’t mandatory," Mulinare says. "For the most part women were given the same information. Dependent on the location, they would view a video and have some discussion."
Between Nov. 5, 2001, and April 24, 2003, some 60,000 women of reproductive age (18-44) were vaccinated against smallpox in three populations: military personnel, U.S. civilian health care and public health workers, and some clinical research study volunteers.
Overall, 103 women inadvertently received smallpox vaccine while pregnant or conceived within four weeks of vaccination.
Historically, approximately 50 cases of fetal vaccinia have been reported in the world and three have been reported in the United States. In 1924, an infant was born prematurely after the mother’s vaccination during a smallpox epidemic. The infant had vaccinia-like skin lesions and died shortly after delivery. In 1968, a premature infant born at 32 weeks to a vaccinated mother had vaccinia-like scars but was otherwise healthy and developed normally. Affected pregnancies have been reported among women vaccinated in all three trimesters and among first-time vaccinees, revaccinees, and among unvaccinated close contacts of vaccinees. No validated prenatal test is available for clinical diagnosis of fetal vaccinia during pregnancy.
Except for fetal vaccinia, smallpox vaccine has not been clearly shown to cause serious birth defects or other adverse events for the fetus or neonate, including premature birth, low birth weight, or miscarriage. Among the general population, 16% to 31% of pregnancies end in miscarriages. While some miscarriages have occurred in the current group of pregnant vaccinees, there is insufficient data to know if their lost pregnancies will exceed that seen in the general population.
"The way the [smallpox] pregnancy register is set up many of the women haven’t gotten even through their first trimester," Mulinare says. "So we can’t really say what the miscarriage rate is relative to the general population. In a general sense, most of the [historical] studies were not able to show any increase in miscarriages. A couple of studies suggested it, but those studies may not have been well enough done to be the basis for saying there is an increase."
[Editor’s note: Health care providers, state health departments, and other public health staff are encouraged to report all exposed pregnant women to the National Smallpox Vaccine in Pregnancy Registry. Civilian women should contact their health care provider or state health department for help enrolling in the registry. Clinicians or public health staff should report civilian cases through their state health department or to the CDC at (404) 639-8253 or (877) 554-4625. Military cases should be reported to DoD at (619) 553-9255. Fax: (619) 553-7601. E-mail: [email protected].]
References
1. Centers for Disease Control and Prevention. Women with smallpox vaccine exposure during pregnancy reported to the National Smallpox Vaccine in Pregnancy Registry — United States, 2003. MMWR 2003; 52(17):386-388.
2. Centers for Disease Control and Prevention. Recommendations for using smallpox vaccine in a pre-event vaccination program: Supplement recommendations of the Advisory Committee on Immunization Practices (ACIP) and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR Dispatch 2003; 52:1-16.
More than 100 pregnant women have been exposed inadvertently to smallpox vaccine since immunization programs began in U.S. hospitals, the military, and clinical trials, the Centers for Disease Control and Prevention reports.
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