The administration of vaccines during pregnancy poses a number of concerns to physicians and patients about the risk of transmitting a virus to a developing fetus. This risk is primarily theoretic. Live-virus vaccines are therefore generally contraindicated in pregnant women. According to the Centers for Disease Control and Prevention (CDC), (1) if a live-virus vaccine is inadvertently given to a pregnant woman, or if a woman becomes pregnant within four weeks after vaccination, she should be counseled about potential effects on the fetus. Inadvertent administration of these vaccines, however, is not considered an indication for termination of the pregnancy.

No evidence shows an increased risk from vaccinating pregnant women with inactivated virus or bacterial vaccines or toxoids. (1) Therefore, if a patient is at high risk of being exposed to a particular disease, if infection would pose a risk to the mother or fetus, and if the vaccine is unlikely to cause harm, the benefits of vaccinating a pregnant woman usually outweigh the potential risks.

Physicians should consider vaccinating pregnant women on the basis of the risks of vaccination versus the benefits of protection in each particular situation, regardless of whether live or inactivated vaccines are used.

Vaccines commonly administered by family physicians, and their indication for use during pregnancy, are summarized in Table 1. (1)

Women of childbearing age often are concerned about whether breastfeeding is safe during immunization. Physicians should reassure their patients that no vaccines are contraindicated during breastfeeding. (1)

Tetanus and Diphtheria

The tetanus and diphtheria toxoids vaccine (Td) is effective in preventing tetanus and diphtheria, two potentially life-threatening conditions. Diphtheria is an infection of the nasal, pharyngeal, laryngeal, or other mucous membranes that can cause neuritis, myocarditis, thrombocytopenia, and ascending paralysis. (2) Tetanus infection can cause production of a neurotoxin, leading to tetanic muscle contractions.

Td toxoid is routinely recommended for susceptible pregnant women. While no evidence exists to prove that tetanus and diphtheria toxoids are teratogenic, (1) waiting until the second trimester of pregnancy to administer Td is a reasonable precaution, minimizing any concern about the theoretic possibility of such reactions. (1) Previously vaccinated pregnant women who have not received a Td vaccination within the past 10 years should receive a booster dose. Pregnant women who are not immunized or only partially immunized should complete the primary series. (1)

Influenza

Fever, malaise, myalgia, and upper respiratory tract symptoms or infections characterize influenza infection. Most severe complications are the result of pneumonia secondary to influenza infection. There are three strains of influenza (A, B, and C), with types A and B responsible for epidemics in the United States.

The influenza vaccine is a killed virus preparation with an annually adjusted antigenic makeup. It should be administered annually between October and December to high-risk patients. The vaccine should be administered to all pregnant women who will be in the second or third trimester of pregnancy during the influenza season (which peaks from December to March in temperate climates but may extend into May in 20 percent of influenza seasons). (3) This recommendation is based on data from pandemics of 1918 and 1957, as well as limited studies done since then demonstrating that women in their second or third trimesters have higher morbidity, similar to other high-risk patients, from influenza infection. (4)

Immunization should be avoided in most patients during the first trimester to avoid a coincidental association with spontaneous abortion, which is common in the first trimester. However, pregnant women with medical conditions that increase their risk for complications from influenza (e.g., asthma, cardiovascular disease, diabetes, suppressed immune system) should be vaccinated before the influenza season regardless of the pregnancy trimester. Studies of influenza immunization with more than 2,000 pregnant women have demonstrated no adverse fetal effects. (1)

Hepatitis A

Hepatitis A infects approximately 100,000 persons annually in the United States, of which 100 die. (5) It is acquired via the fecal-oral route by person-to-person contact or ingestion of contaminated food or water.

Hepatitis A vaccines are derived from viruses grown in diploid cell cultures and are formalin inactivated. (5) Safety of hepatitis A vaccination during pregnancy has not been determined. Because hepatitis A vaccine is produced from inactivated virus, the risk to the developing fetus is expected to be low. Therefore, theoretic risks of vaccination should be weighed against the risk for hepatitis A infection in pregnant women who may be at risk for exposure. Examples calling for immunization include travel to endemic areas or intravenous drug use during pregnancy. (6)

Finally, if a pregnant woman is exposed to hepatitis A, administration of immune globulin is strongly recommended; this agent is considered safe during pregnancy and is more than 85 percent effective in preventing acute hepatitis infection. (3)

Hepatitis B

Hepatitis B infection is caused by a DNA-containing virus and is transmitted through contact with infected blood, sexual activity, and sharing of intravenous needles. Hepatitis B infection may be asymptomatic, or it may result in fulminant hepatitis.

The risk of developing chronic illness associated with complications of cirrhosis, hepatocellular carcinoma, and a chronic carrier state has been a key factor in the recommendation for universal vaccination of all children. Vaccination should also be offered to any interested adult and strongly recommended to those at risk. (2) Risk factors for a pregnant woman include having had sex with a man who has sex with men, having multiple sexual partners, using or abusing intravenous drugs, having occupational exposure, and being a household contact of acutely infected persons or persons with a chronic carrier state.

The hepatitis B vaccine contains viral surface antigen produced by recombinant DNA technology. It is administered in three doses, at birth and at one and six months of age, and has minimal to no side effects. Because it contains noninfectious hepatitis B surface antigen particles and should cause no risk to the fetus, neither pregnancy nor lactation is a contraindication to vaccination. (1)

Pneumococcal

Streptococcus pneumoniae is a gram-positive diplococcal bacterium that is a major cause of pneumonia, meningitis, and bacteremia. Risk factors for pneumococcal infection in pregnant women include diabetes, cardiovascular disease, asplenia, immunodeficiency, asthma, and other respiratory diseases.

The current vaccine includes purified capsular polysaccharide from the 23 most common types of S. pneumoniae. It is recommended by the CDC for use in adults with any of the aforementioned risk factors. (3)

The Advisory Committee on Immunization Practices (ACIP) currently recommends that women at high risk be given this vaccination before, but not during, pregnancy. The safety of the pneumococcal vaccine during pregnancy has not been evaluated, although no adverse consequences have been reported among newborns whose mothers were inadvertently vaccinated. (1)

Polio

Poliovirus is an enterovirus with three different strains that cause disease. Exposure may result in asymptomatic infection as well as nonparalytic and paralytic disease. Asymptomatic patients can transmit the disease to susceptible persons. The disease continues to be a problem worldwide, but all recent domestic polio cases have been caused by the strains of virus found in the oral polio vaccine (OPV). This situation has resulted in a change in the ACIP's recommendation for use of inactivated polio vaccine (IPV), instead of OPV or a combination of OPV-IPV for all routine vaccinations. (1) IPV is inactivated by formaldehyde, and its use has eliminated vaccine-associated polio infection. (7)

Although no adverse effects have been documented with OPV or IPV in pregnant women or their fetuses, both vaccines should be avoided during pregnancy on a theoretic basis. However, the CDC states that IPV may be administered in accordance with the recommended schedules for adults if a pregnant woman is at increased risk for infection and requires immediate protection against polio. (1) Situations that might warrant immediate protection in pregnancy include possible occupational exposure or travel to areas of endemic polio. The 2003 recommended immunization schedule for adults is available online at www.aafp.org/x14956.xml.

Varicella