Health officials probe ‘inadvertent’ vaccinations of pregnant women

ATLANTA — According to the CDC’s National Smallpox Vaccine in Pregnancy Registry, 103 women did not know they were pregnant or conceived within four weeks following vaccination with smallpox vaccine — and CDC and FDA officials have launched an investigation into why.

	Background is vaccinia virus/Source: CDC

CDC officials reported their experience with the registry in a recent Morbidity and Mortality Weekly Report. While the CDC did note that some women inadvertently vaccinated had a negative pregnancy test on the day of their vaccinations, they said they are investigating further.

CDC researchers said that between Dec. 13, 2002 and April 22, 2003, 62,222 women of reproductive age were screened for previous smallpox vaccination, and 52,185 were vaccinated in the military’s smallpox immunization program. Of those, 85 were inadvertently exposed to smallpox vaccine during pregnancy. “On the basis of the estimated date of conception, 62 women conceived before vaccination and 23 conceived during the four weeks after vaccination,” the researchers wrote.

Regarding civilians, CDC researchers wrote that between Jan. 24 and April 24, 2003, 6,174 women of reproductive age were vaccinated through the civilian program, and six were inadvertently exposed to smallpox vaccine during pregnancy. Among that group, two women conceived within one week before vaccination and four conceived during the four weeks after vaccination. The study team noted that two of the women had miscarriages during early pregnancy.

Some pregnant women participating in clinical trials also were exposed to smallpox vaccines. During November 2001 to April 24, 2003, 12 women from clinical studies who had inadvertent exposure to smallpox vaccines during pregnancy have been reported to the registry. The researchers noted however, in those cases, each of the women had a negative pregnancy test on the day of vaccination.

The researchers said that while the vaccine is contraindicated in women who are pregnant, inadvertent exposures have occurred.

The CDC set up the registry as a way to monitor inadvertent vaccination, and any adverse events as a result. Smallpox vaccine can cause fetal vaccinia, and 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. Unfortunately, the researchers wrote, “no validated prenatal test is available for clinical diagnosis of fetal vaccinia during pregnancy.”

However, despite the risk of fetal vaccinia, CDC officials said, “inadvertent exposure of pregnant women to smallpox vaccine should not be a reason to consider pregnancy termination because the risk for fetal vaccinia is low.”

Question about pregnancy

Health officials recommend that all pre-event smallpox vaccination programs include pregnancy screening and questioning about the possibility of pregnancy before and after vaccination.

In the report, CDC officials recommended counseling vaccinees about “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.”

The researchers said the registry seems to show that smallpox vaccination screening and education in the vaccination programs appear to be working.

Using those numbers as a basis for calculation, the researchers said both the estimated rate of unknown pregnancy and the rate of conception during a four-week period is 6:1,000 reproductive-aged women. “Therefore, in the absence of screening and counseling, an estimated 12:1,000 reproductive-aged women vaccinees could be expected to be exposed to smallpox vaccine during pregnancy,” the researchers wrote. “Assuming that health care providers have the same age-specific fertility rates as the general population, when this rate is adjusted to the older age distribution of the civilian health-care workers currently vaccinated, an estimated four per 1,000 women would be pregnant and not know it and an additional four per 1,000 would be expected to conceive during the four weeks after vaccination. The rate of inadvertent exposure during pregnancy among women of reproductive age vaccinated during the first stage of the civilian and DoD (Department of Defense) programs is approximately one per 1,000.”

They noted that their calculated rate is “substantially lower than the approximately eight per 1,000 women and 12 per 1,000 women who would be inadvertently exposed to smallpox vaccine in the civilian health-care worker population and in the general population, respectively, in the absence of screening and education.”

As a result of the registry data, researchers said the U.S. military revised education materials for potential vaccinees and expanded the questions about pregnancy and intention to become pregnant on screening forms. The FDA has also has enhanced pregnancy screening materials and protocols.

Also, the CDC is reviewing and evaluating existing recommendations for pregnancy screening and education in the civilian smallpox vaccination program. Both the CDC and the DoD are investigating the inadvertent vaccinations, and the CDC wrote, “information from these investigations is expected to guide efforts to improve the pregnancy screening and education components of the smallpox vaccination programs.”

Reporting cases

In the meantime, CDC officials are encouraging clinicians and public health staff to report civilian cases through their state health department or to the CDC, telephone 404-639-8253 or 877-554-4625. Military cases should also be reported, by calling 619-553-9255, DSN 553-9255, fax 619-553-7601 or e-mail code25@nhrc.navy.mil.

The CDC has also asked that health care providers save and forward fetal tissue from miscarriages for vaccinia testing to the CDC. Laboratories should freeze specimens at –94^º F (–70^º C), preferably in viral transport media. Clinicians can contact the registry for additional information about forwarding laboratory specimens.

For more information:

• CDC. Women with Smallpox Vaccine Exposure During Pregnancy Reported to the National Smallpox Vaccine in Pregnancy Registry - United States, 2003. MMWR. 2003;52(17):386-388.