Mothers protect their children in a variety of ways. One of the best ways is often ignored, and for no good reason.
Babies leaving the womb confront a tidal wave of germs, which can occasionally overwhelm them. For example, every year about 25 babies in the U.S.—all less than 2 months of age—die from pertussis (whooping cough). Because infants don’t receive their first dose of pertussis vaccine until they are 2 months old, and because one dose of vaccine wouldn’t be protective, the pertussis vaccine doesn’t prevent any of these deaths. Nonetheless, all of these babies could have been saved.
How?
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During the third trimester of pregnancy, mothers transfer antibodies from their own bloodstream to their baby’s. Indeed, at the time of birth, the concentration and specificity of antibodies in the newborn’s blood are virtually identical to their mother’s.
For this reason, a few years ago the Centers for Disease Control and Prevention (CDC) recommended that all pregnant women receive the pertussis vaccine (Tdap) during the third trimester. Mothers immunized with Tdap make antibodies against pertussis that they then transfer to their babies. And it works. More than 90 percent of young infants whose mothers got the pertussis vaccine are protected against disease.1,2 The reason that babies in the United States still die from pertussis is that most mothers don’t get the vaccine. In a recent survey of 16 states and New York City, only 10 percent of pregnant women chose to protect their unborn child.3
Pertussis isn’t the only vaccine recommended for pregnant women.
Starting in the 1960s, the influenza vaccine was also recommended during pregnancy. Three compelling facts dictated this recommendation: (1) pregnant women are more likely to be hospitalized and die from influenza than women of the same age who aren’t pregnant;4 (2) influenza infections during pregnancy can affect the unborn child, causing spontaneous abortions, premature births, and low birth weights;5 and (3) infants under 6 months of age are more likely to have severe complications or die from influenza than any other age group.6 Given that the influenza vaccine isn’t recommended for children less than 6 month of age, the only way that young infants can be protected in the first few months of life is by maternal immunization. Although the influenza vaccine is safe, protects against severe outcomes in both the mother and the child, and is readily available in clinics and pharmacies, only about 50 percent of pregnant women choose to get it.7
Three other maternal vaccines would also be of value.
One vaccine in the pipeline prevents a bacterium called group B strep (group A strep is the one that causes sore throats; this is a different one). In the 1980s, researchers found that about 20 percent of women were colonized with group B strep, meaning that the bacteria were living harmlessly on the surface of their rectum or vagina. However, when babies traveling through the birth canal came in contact with these bacteria, they developed bloodstream infections (sepsis) or meningitis, both of which can cause permanent harm or death. Thousands of children suffered these infections in the United States every year. In response, by the 1990s, all pregnant women were tested to make sure that they weren’t colonized with group B strep. If they were, then they received antibiotics to rid the bacteria. This strategy reduced, but didn’t eliminate, group B strep infections; indeed, antibiotics had no effect on group B strep infections that occurred between 7 days and 3 months of age. Early trials of a group B strep vaccine in pregnant women have shown that it is safe and highly immunogenic. Although it is not yet available, a group B strep vaccine for pregnant women is right around the corner. 8
Another vaccine for pregnant women could prevent a disease that causes more hospitalizations and more deaths than any other childhood infection: respiratory syncytial virus or RSV. RSV causes severe bronchiolitis and pneumonia in premature babies and very young infants, too young to be protected by a childhood vaccine. Again, immunizing pregnant women would be the best strategy. One company (Novavax) has begun clinical trials in pregnant women to determine whether the vaccine is safe and effective.9,10 When available, the RSV vaccine will be a lifesaver.
The fifth vaccine, which prevents meningococcus, is currently recommended for all 11 to 13 year olds in the United States. Most parents would probably be surprised to learn that infants are 17 times more likely to be infected with meningococcus than teenagers. Unfortunately, the companies that make the meningococcal vaccine haven’t pushed to do clinical trials in pregnancy, even though this strategy would likely prevent hundreds of cases of a potentially devastating infection.
Nature has provided a mechanism for mothers to protect their babies both before and immediately after they leave the womb. But as Dr. Walter Orenstein, the former director of the National Immunization Program, has said, “There’s a difference between vaccines and vaccination.” If you don’t get them, they don’t work.
References
1. Amirthalingam, G., N. Andrews, N. Campbell, et al., “Effectiveness of maternal pertussis vaccination in England: an observational study,” Lancet (2014) 384: 1521-1528.
2. Dabrera, G., G. Amirthalingam, Andrews, N., et al., “A case-control study to estimate the effectiveness of maternal pertussis vaccination in protecting newborn infants in England and Wales, 2012-2013,” Clinical Infectious Diseases (2015) 60: 333-337.
3. Ahluwalia, I.B., H. Ding, D. D’Angelo, et al., “Tetanus, diphtheria, pertussis vaccination coverage before, during, and after pregnancy—16 states and New York City, 2011,” Morbidity and Mortality Weekly Report (2015) 64: 522-526.
4. Creanga, A.A., L. Kamimoto, K. Newsome, et al., “Seasonal and 2009 pandemic influenza (H1N1) virus infection during pregnancy: a population based study of hospitalized cases,” American Journal of Obstetrics and Gynecology (2011) 204: supplement 1:S38-S45.10-18.
5. Mosby, L.G., S.A. Rasmussen, and D.J. Jamieson, “2009 pandemic influenza A (H1N1) in pregnancy: a systematic review of the literature,” American Journal of Obstetrics and Gynecology (2011) 205: 10-18.
6. Bhat, N., J. G. Wright, K.R. Broder, et al., “Influenza-associated deaths among children in the United States, 2003-2004,” New England Journal of Medicine (2005) 353:2559-2567.
7. Ding, H., C.L. Black, S. Ball, et al., “Influenza vaccine coverage among pregnant women—United States, 2014-15 influenza season,” Morbidity and Mortality Weekly Report (2015) 64: 522-526.
8. Madhi, S.A., C.L. Cutland, L. Jose, et al., “Safety and immunogenicity of an investigational maternal trivalent group B streptococcal vaccine in healthy women and their infants: a randomized phase 1b/2 trial,” Lancet Infectious Diseases (2016) 16: 923-934.
9. RSV vaccine snapshot. PATH Vaccine Resource Library, 2016.
10. Omer, S.B., “Maternal immunization,” New England Journal of Medicine (2017) 376: 1256-1267.
Paul A. Offit, MD is a professor of pediatrics and director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and the author of Pandora’s Lab: Seven Stories of Science Gone Wrong (National Geographic Press, April 2017)
