FA16 Immunization Module’s Updates

Vaccinating Pregnant Women

 

Vaccinating pregnant women

There are two key reasons that pregnant women should receive vaccines: to bolster their own immune system which may be affected by the pregnancy, and to provide immunological protection for the fetus via passive immunization.

The two major vaccines recommended by the CDC for pregnant women are:

1. The seasonal flu vaccine
2. Whooping cough vaccine (MMR before pregnancy, Tdap during pregnancy)

Maternal Immune Protection

Effects of Pregnancy on Maternal Immunity

For nearly 50 years, physicians held the (mostly false) belief that the implantation of an embryo leads to suppression of the maternal immune response. This assumption was based on the idea that the placenta and fetus are “foreign” cells, similar to an organ transplant, that would be targeted by maternal immune cells if they were not suppressed. However, this does not correlate well with the evolutionary importance of pregnancy in terms of the conservation of the species—the immune system should be bolstered during this time period, not suppressed. Thus, today, the immunological relationship between the mother and fetus is more accurately described as a “unique immune condition that is modulated, but not suppressed” [1].

Even so, the increased levels of progesterone during pregnancy can negatively impact both the innate and adaptive immune responses. This hormone impairs natural killer cell activity, suppresses the synthesis of lymphocytes, and increases the production of non-effector antibodies that block fetal antigens [2]. In addition to the direct effects of pregnancy on the immune system, changes to the cardiovascular and pulmonary systems can increase a pregnant woman’s likelihood of infection [3].

Vaccination during pregnancy

Because of these modulations to maternal immunity, the CDC recommends that all pregnant women receive the seasonal flu vaccine by the end of October [4]. This helps to protect the mother from infection, which can be dangerous or even fatal if her immune system is compromised, and also prevents adverse effects of the virus on the fetus, including premature labor and birth defects.

Pregnant women should not receive the nasal spray version of the flu vaccine due to the possibility of maternal immunocompromisation [5].

Fetal Immune Protection

Fetal and Neonatal Immunity

The fetal immune system lacks antigenic experience because it develops in a sterile environment [6]. Because of this, newborns are particularly susceptible to viral, bacterial, and fungal infections in the first few months of life.

The fetus is protected from infection by the mother’s immune system as well as IgG antibodies that pass through the placenta. After birth, IgA antibodies pass through the breast milk to the neonate to provide passive immunity.

Since the fetus and neonate receive the majority of their immune protection from maternal sources, it is imperative that the mother develop antibodies to pathogens that are particularly dangerous to the infant.

Vaccination Before and During Pregnancy

According to the CDC, the most important preventive vaccine for pregnant women to receive is the Whooping Cough (Pertussis) vaccine [4]. Whooping cough is fatal in up to 20 newborns per year in the United States, and nearly half of infants who are less than 1 year old who are infected with pertussis will need treatment in the hospital [4].

Before pregnancy, it is recommended that women receive the MMR vaccine to obtain immunity to pertussis. However, during pregnancy, it is better for women to receive the Tdap vaccine because the measles and mumps components of MMR are live, attenuated viruses. When the mother generates antibodies against the whooping cough pathogen, immunity will be transferred to the fetus via the placenta and to the newborn through breast milk. This passive immunity can be life-saving for immunocompromised infants. Women should receive the Tdap vaccine during each pregnancy, since the number of antibodies against pertussis decreases over time.

Summary of Vaccine Schedule for Pregnant Women [7]

Resources

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3025805/

[2] https://www.ncbi.nlm.nih.gov/pubmed/10916936

[3] http://www.cdc.gov/vaccines/pregnancy/downloads/pregnancy-vaccination.pdf

[4] http://www.cdc.gov/vaccines/pregnancy/pregnant-women/

[5] http://www.cdc.gov/flu/protect/vaccine/pregnant.htm

[6] http://www.uptodate.com/contents/immunity-of-the-newborn

[7] http://www.health.state.mn.us/divs/idepc/immunize/images/pregvax.gif 

 

 

 

 

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