PROTOCOLS OB/GYN INFECTION

Immunization in pregnancy

By Marvin S. Amstey, MD

Here's an update on when and how to use tetanus, HBV, influenza, and other vaccines during pregnancy.

Although vaccination of pregnant women is an uncommon preventive measure, the need for active and passive immunization in pregnancy is becoming greater with more rapid dissemination of infectious agents due to improved transportation and expanding travel. The following discussion covers broadly relevant issues and specific vaccines that are more frequently used (Tables 1 and 2).

TABLE 1
Vaccines available for active immunization

TABLE 2
Passive immunization materials

Active immunization

The accepted criteria for the use of active immunization are susceptibility to the infection and absence of antibodies. Since routine antibody testing is not done except for rubella and hepatitis B infections, a person's susceptibility is usually unknown. Therefore, it is important for you to get a history and record of previous vaccinations. Fortunately because of state vaccination requirements for school admissions, most women of childbearing age in the United States should be immune to measles, mumps, polio, rubella, tetanus, pertussis, diphtheria, and probably hepatitis B. However, assume immunity to tetanus and diphtheria only if the last booster injection of vaccine was given less than 10 years ago.

In general, the most conservative statement on the subject—"avoid vaccination in pregnancy with any live bacterial or viral product"—is a safe guideline. But while in the past this interdiction was applied to all immunizing products, it should now exclude nonviable bacteria, bacterial products, inactivated viruses, and toxoids. In fact, it is proper management to update a pregnant patient's tetanus and (during the flu season) influenza immunization.

Some physicians have a theoretical fear that introducing an antigen such as a vaccine into the mother will make the fetus tolerant and therefore unable to form antibodies. While this kind of tolerance can be found in some animals, it has never been seen in humans. In fact, a trial of maternal vaccination with Haemophilus influenzae type B (HIB) provided newborns with high antibody levels. Current studies are showing the same thing for Group B streptococcus, pneumococcus, and respiratory syncytial virus (RSV). Moreover, when infants whose mothers had been immunized with HIB during pregnancy were subsequently vaccinated at 18 months of age, they had the same boost in antibodies as observed for infants of nonvaccinated mothers.

Tetanus. The most commonly used vaccine for active immunization—for both pregnant and non-pregnant patients—is tetanus. If someone has never been vaccinated, or more than 10 years has elapsed since vaccination, the product of choice is the adult formulation of tetanus combined with diphtheria (that is, the adsorbed toxoids of these bacteria).

Primary vaccination is given as two doses, 1 month apart, followed by a third dose, 6 to 12 months after the second. The booster dose is a single 0.5-mL injection every 10 years.

If the patient does not have immunity, the vaccine should be part of prenatal care. It is well known that this therapy prevents neonatal tetanus, which, although very rare in the US, is an important cause of neonatal mortality in the developing world. A 90% reduction in mortality from neonatal tetanus in Sri Lanka was achieved from 1978 to 1983 by immunizing all pregnant women with tetanus toxoid.

Hepatitis B infection. Perhaps the second most common reason for vaccination in pregnancy is the need either for primary immunization against hepatitis B virus (HBV) infection because of family, sexual, or work exposure to this virus or for continuing a series of HBV injections that were begun before conception. Although this vaccine—for that matter, any vaccine—is not approved by the Food and Drug Administration for use in pregnancy, its benefits outweigh any potential risk in certain situations. It is good medical practice to offer it or continue its use in women at high risk of contracting the disease.

There has been no reported harm from HBV vaccine in pregnancy. The vaccine is administered as two 1-mL IM injections 2 months apart, with a third dose given 6 months after the second.

Influenza. The Centers for Disease Control and Prevention (CDC) now recommends that the current influenza vaccine be given to any pregnant woman who will be in her second or third trimester or early puerperium during the "flu" season, which is November though March.

Physicians should consult local public health officials to learn which variety of influenza vac-cine is recommended. Type B influenza virus always is the same strain, but type A influenza virus changes its antigenic makeup frequently, making last year's vaccine less effective than the current one.

Poliomyelitis. Although no adverse effects of oral or IV poliomyelitis vaccine have been documented among pregnant women or their fetuses, the CDC recommends avoiding vaccination of pregnant women. However, if a pregnant woman requires immediate protection against poliomyelitis, she may be administered either the oral or parenteral vaccine in accordance with the recommended schedules for adults.

Typhoid. There is little call for typhoid vaccine, particularly in pregnancy, unless the woman is traveling to an endemic area or one where the water supply is affected by a natural disaster. In such situations, it is safe to give typhoid vaccine either as a primary series of two injections, 4 weeks apart, or as a single booster dose if primary vaccination has been done within 5 years. The new oral formulation of typhoid vaccine is better tolerated.

Other vaccines. All other available vaccines are used so infrequently in pregnancy that one needs to contact public health officials for proper product and dose. It is self-evident that exposure to a life-threatening disease, even in pregnancy, warrants making an exception and even using live vaccines, such as those for rabies or yellow fever.

The CDC no longer maintains a registry of women who receive measles-mumps-rubella virus vaccines 3 months before or after conception. This registry allowed the CDC to inform the medical community about such things as inadvertent rubella vaccination during pregnancy. It has enabled us to learn, for example, that administering live but attenuated rubella virus vaccine, once thought to be a potential tragedy, actually poses very little or no risk to a developing fetus.

Merck & Company currently maintains a registry for reporting the inadvertent administration of varicella-zoster vaccine to pregnant women.

Passive immunization

There is no contraindication to using any immunoglobulin or serum in pregnancy. The danger of serum sickness from using horse serum in a pregnant woman is the same as for a nonpregnant woman and calls for the same precautions. Passive immunity is accomplished with heterologous antibody, which is metabolized with a finite half-life. Protection is therefore limited, usually to 30 days.

It is necessary to use passive immunization when a woman is exposed to an infectious agent or toxin and time doesn't allow her to develop her own antibody by active immunization. For example, splashing of HBV-contaminated blood in an eye requires immediate passive immunization to provide antibodies without delay. This measure must be followed by active immunization to provide long-lasting immunity.

Future developments

In addition to protecting the mother, immunization in pregnancy may also protect the newborn against infectious agents likely to cause serious harm soon after birth or in the first few months of life. Examples are group B streptococcal infection, RSV, and invasive H influenzae infection. Maternal vaccination in these instances may confer passive immunity on the fetus and newborn because immunoglobulin G antibodies produced by the mother will cross the placenta.

The Vaccine Act passed by Congress in 1986 requires physicians to maintain accurate records, including lot numbers, of any vaccinations with diphtheria- pertussis-tetanus, oral polio, measles-mumps-rubella, and HIB vaccines. The Vaccine Act also requires reporting any untoward reactions to public health officials. While these four vaccines have no regular role in obstetrics at this point, this requirement should apply to all immunizing agents. Other recommendations regarding adult immunization are available from the CDC and the American College of Physicians.

SUGGESTED READING

Advisory Committee on Immunization Practices (ACIP). General recommendations on immunization. MMWR. 1989;38:205-214.

Advisory Committee on Immunization Practices (ACIP). Poliomyelitis prevention in the United States: introduction of a sequential vaccination schedule of inactivated poliovirus vaccine followed by oral poliovirus vaccine. MMWR. 1996;46(RR-3):18.

Advisory Committee on Immunization Practices (ACIP). Update: vaccine side effects, adverse reactions, contraindications, and precautions. MMWR. 1996;45(RR-12):1-35.

American College of Obstetrics and Gynecology. Immunization during pregnancy. ACOG Technical Bulletin Number 160—October 1991. Int J Gynaecol Obstet. 1993;40:69-79.

American College of Physicians. Guide for Adult Immunization. 3rd ed. Philadelphia, Pa; 1994.

Amstey MS. Vaccination in pregnancy. Clin Obstet Gynecol. 1983;10:13-22.

Amstey MS, Insel R, Munoz J, et al. Fetal-neonatal passive immunization against Hemophilus influenzae, type b. Am J Obstet Gynecol. 1985;153:607-611.

Amstey MS, Insel RA, Pichichero ME. Neonatal passive immunization by maternal vaccination. Obstet Gynecol. 1984;63:105-109.

Baker C, Rench M, Edwards M, et al. Immunization of pregnant women with a polysaccharide vaccine of group B streptococcus. N Engl J Med. 1988;319:1180-1185.

Centers for Disease Control and Prevention. Prevention and control of influenza. MMWR. 1996;45(RR-5):5-6.

Ramalingaswami V. Importance of vaccines in child survival. Rev Infect Dis. 1989;11(Suppl 3):S498-S502.

Dr. Amstey is Professor Emeritus, Department of Obstetrics and Gynecology, University of Rochester School of Medicine and Dentistry, Rochester, N.Y., and a former President of the Infectious Diseases Society for Obstetrics and Gynecology.

Adapted from Mead PB, Hager WD, Faro S, eds. Protocols for Infectious Disease in Obstetrics and Gynecology. 2nd ed. Malden, Mass: Blackwell Science Inc; 2000.

Flu season 2000-2001: Vaccine may be scarce

Manufacturers expect delays in influenza vaccine shipments this year and there may be less vaccine available than in past flu seasons. Because of this, the Advisory Committee on Immunization Practices of the Department of Health and Human Services is recommending that health-care providers consider delaying adult mass flu vaccination campaigns until November, rather than starting in October as usual.

Whether a shortfall will occur is uncertain at this time, but if it does, the vaccine should be administered first to people at high risk for developing serious complications from influenza. Women who will be in the second or third trimester of pregnancy during the flu season are in this high-risk category.

This year's vaccine contains two new influenza type A strains, A/Panama/2007/99-like (H3N2) and A/New Caledonia/20/99-like (H1N1). The third strain, B/Yamanashi/166/98-like virus, is unchanged from last year. One reason for the delay and potential shortage is that the A (H3N2) strain has not grown as well as the corresponding strain used for the 1999-2000 vaccine. This and other flu vaccine information is available on the Centers for Disease Control and Prevention Web site, http://www.cdc.gov (accessed 8/30/2000).

 

Marvin Amstey. Immunization in pregnancy. Contemporary Ob/Gyn 2000;10:65-72.