While most people are familiar with fist bumps and baby bumps, few are aware of the mommy bump. The mommy bump refers to the bump in protection that babies receive when their mothers receive their Tdap (tetanus, diphtheria, acellular pertussis) and flu vaccines during pregnancy.

Babies need all the protection they can get. Their developing immune systems aren’t good at fending off germs like whooping cough and flu. In the same way, their developing immune systems react only weakly to vaccines, so they must be given multiple doses to develop protection. Babies aren’t fully defended against whooping cough until a month after they’ve received three vaccine doses. Therefore, a baby on the recommended schedule isn’t fully covered until 7 months of age. Likewise, babies don’t respond to the flu vaccine until 6 months of age, and must receive two doses a month apart to be protected. In other words, babies are vulnerable until they’re about 7 months of age.

The whooping cough and flu are both dangerous for babies. Pertussis is the bacteria that causes whooping cough and like the flu is spread through coughing and sneezing. The disease often goes unrecognized as not everyone develops the telltale whoop, making it difficult to keep it from spreading. Half of babies with whooping cough require hospitalization and one out of every hundred hospitalized will die. Those younger than 6 months are most likely to suffer serious complications such as pneumonia and brain inflammation. Similarly, many babies are hospitalized each year with the flu for breathing problems, pneumonia and dehydration.

So, how does the mommy bump help protect young babies? After being vaccinated, the pregnant mother produces high levels of antibodies that peak after about two weeks. These antibodies are actively transferred to the unborn baby around the beginning of the third trimester. The antibodies slowly fall after birth, providing protection for the first four to six months. Breastfeeding tends to prolong the protection as antibodies continue to pass from the mother to baby in breast milk.

The Centers for Disease Control recommends that women receive a Tdap vaccine as early as possible in the window from the 27th to 36th week of each pregnancy. This way the mother’s antibody levels are highest during antibody transfer, giving the baby the biggest boost. It’s also better to be vaccinated early in the window in the case that the baby is born early. The more antibodies the baby starts with, the stronger the protection.

The recommendation is a little different for the flu vaccine. Pregnant women should receive the vaccine as early in the flu season as possible. Pregnant women are much more likely to become gravely ill or die from the flu due to the demands pregnancy places on their body and immune system. Even when given early, the flu vaccine still results in more antibodies for the baby.

The mommy bump helps protect babies during the vulnerable period from birth to 6 months old.

Vaccine Smarts is written by Sealy Institute for Vaccine Sciences faculty members Drs. Megan Berman, an associate professor of internal medicine, and Richard Rupp, a professor of pediatrics at the University of Texas Medical Branch. For questions about vaccines, email vaccine.smarts@utmb.edu.

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