During the first month of life, an infant is very susceptible to infection and disease because the immune system is not yet fully developed. It is questionable how effective vaccines are at this time. Most vaccines are given after a month has passed and the immune system is prepared to use a vaccine effectively. But during that first month of life, an infant may be in danger of contracting a serious disease. The only protection available to the neonatal child is protection from the mother. Immunizing pregnant women who have not previously been vaccinated provides a way to protect the infant during that sensitive time.
Immunoglobulin G is the only antibody, and one of the few substances that can pass through the placenta. The placenta is a sack surrounding the fetus that protects it from potential toxins in the mother’s environment. It lets through the nourishment that the fetus needs and also lets through other important elements to the fetus’s health including antibodies. Any antibodies that the mother has will be passed to the fetus. Even vaccination during pregnancy ensures that these antibodies are passed to the fetus. Immunizing pregnant women is one of the last efforts available to protect the infant in the first month of life.
Extensive studies have been done on immunizing pregnant women with tetanus, diphtheria, and pertussis. These successfully passed through the placenta and protected the infants at birth and beyond. Antibodies are also present in breast milk and can provide protection longer than the neonatal period. Infants can be protected by breast milk up to six months after birth. However, passive immunity does not last forever and the infants must be immunized and acquire their own antibodies eventually. A fully developed immune system is achieved usually a month after birth and vaccines can be given throughout childhood to help build up immunity without suffering the illness itself.
Passive immunity achieved by immunizing pregnant women can also protect against bacterial infections. Bacterial infections can be quick and deadly for neonates. A mother that has successfully overcome bacterial infections carries antibodies against them and when exposure happens during the first month of life, the infant is protected by passive immunity. Breast milk also aids in this process during the first three to six months of life. After that period, the infant will begin to develop immunity on its own as it is exposed to different bacteria. At an older age, the infant can handle the exposure far better than right after birth.