A vaccine is usually an injection, which improves the immunity to a particular disease. It is works by including an agent that closely resembles the disease-causing pathogen, but in a weakened or killed form.

This subsequently stimulates the immune system to recognize this weakened or killed pathogen as ‘foreign’ to the body. As a result, the immune system will kill the pathogen from the vaccine and ‘remember’ how it did it, so the next time this pathogen enters the body, it will be recognized and killed easily by the white blood cells.

Vaccines and Pregnant Women

Research has shown that vaccinating pregnant women also protects their babies from the pathogen that is present in weakened or filled form in the vaccine.

In order to test this hypothesis, pediatricians tested babies up to six months old that were hospitalized for the flu or for other reasons. For all these babies, the researchers checked whether the mother had received a vaccine against the flu during their pregnancy.

It turned out that over 90% of the babies from mothers that were vaccinated against the flu were also protected against the flu.

Baby Immunity

This result can have important implications, because babies younger than six months cannot be vaccinated efficiently themselves. Babies under this age with medical conditions that usually require a vaccine are now protected by what is called a ‘cocoon vaccination’, which is the vaccination of all the family members, to prevent the baby from being exposed to the pathogen.

Another source of baby immunity are the antibodies of the mother the babies received through the placenta. A last source of potential antibodies for babies younger than six months is through breast feeding, which can also transfer antibodies from the mother to her child.

As soon as the six month mark has passed, the baby begins developing his or her own immune system and his or her own antibodies.

So, vaccinating a pregnant woman allows this woman to develop antibodies against a certain pathogen (say, the flu). These antibodies can be transferred to the baby in her womb, which protects the child for the first six months of his or her life.

References

Benowitz, I.; Esposito, D.B.; Gracey, K.D.; Shapiro, E.D. & Vasquez, M. (2010). Influenza Vaccine Given to Pregnant Women Reduces Hospitalization Due to Influenza in Their Infants. Clinical Infectious Disease. 51(12), pp. 1355 – 1361.
Goodman, A. (2009). Seasonal Flu vaccine for Pregnant Mothers Protects Infants. 47th Annual Meeting of the Infectious Diseases Society of America (IDSA): Abstracts LB-11, 703, and 704.
Schlaudecker, E.P. & Steinhoff, M.C. (2010). Helping Mothers Prevent Influenza in Their Infants. Pediatrics. 126(5), pp. 1008 – 1011.