Influenza is the leading cause of vaccine-preventable deaths in the United States. In children, the highest incidence of hospitalization due to influenza is among infants younger than 1 year, with those younger than 6 months at highest risk. Pregnant women with influenza also have a greater risk of serious problems developing for their unborn baby, including premature labor and delivery.
Influenza vaccine is recommended by the US Centers for Disease Control and Prevention (CDC) for all pregnant women and children; however, no vaccine is approved for infants younger than 6 months. The recommended strategies for reducing influenza risk in this vulnerable young infant age group are: 1) immunization of the caregivers and family of the young infant, and 2) flu vaccination of the pregnant woman.
How does mom's flu shot protect her baby?
After getting vaccinated, a pregnant woman’s body creates specialized proteins called antibodies, which recognize flu viruses and boost the body's defenses against these pathogens. The protective antibodies made in the pregnant woman’s body are transferred to the baby. Flu antibodies are a "gift the mom gives her baby across the placenta," says Dr. Julie Shakib, a pediatrician at the University of Utah School of Medicine who led a study published in the journal Pediatrics. The study showed that infants born to women who had a flu vaccine during pregnancy had reductions of 70% for laboratory-confirmed influenza and 81% for influenza hospitalizations in their first 6 months.
A study from South Africa published in the New England Journal of Medicine suggested that vaccines given to mom can be transferred to baby, regardless of HIV status. Another prior study has shown that babies do benefit from maternal immunization - including a 2008 trial in Bangladesh that showed a 63% reduction in influenza illness among infants born to vaccinated mothers and a 36% reduction in the number of serious respiratory illnesses to both mothers and infants. “Our study shows that a newborn’s risk of infection can be greatly reduced by vaccinating mom during pregnancy. It’s a two for one benefit,” said Dr. Mark Steinhoff, the study’s senior author and professor at the Bloomberg School’s Department of International Health.
How safe is the influenza vaccine in pregnancy?
The influenza vaccine is a killed vaccine and cannot replicate or cause influenza in a person who is vaccinated. Vaccines are developed with the highest safety standards. The US Food and Drug Administration approves all vaccines while the CDC continues to monitor all vaccines after they are approved. The currently available vaccines have been used for many years in millions of pregnant women and are not known to cause pregnancy problems or birth defects. There is a large body of scientific studies that supports the safety of flu vaccine in pregnant women and their babies.
Flu vaccine may protect infants against more than just flu
The benefits of vaccinating women against flu during pregnancy extend beyond influenza to protecting young infants against acute respiratory infections from bacterial causes. Investigators based in South Africa reported in Clinical Infectious Diseases analyzed the efficacy of flu vaccination of pregnant women and their babies during their first 6 months of life. When they looked at all-cause acute lower respiratory tract infection (ALRI), hospitalization incidence was lower in the babies of moms who had received the flu vaccine. Of 30 ALRI hospitalizations in the first 3 months of life, 9 were in the group given the flu vaccine and 21 were in the group not given the flu vaccine, for a vaccine efficacy of 57.5%. The investigators concluded that flu vaccination during pregnancy may protect against bacterial infections in early infancy, given that flu infection predisposes patients to secondary illness.
The CDC, the American College of Obstetrics and Gynecology, and the American Academy of Pediatrics recommend that all women who are pregnant during flu season get a flu shot regardless of their trimester.