The Tdap vaccine (Tetanus, Diphtheria, and Pertussis) is a combined immunization routinely recommended for adults, including pregnant individuals, to prevent three specific bacterial infections. Respiratory Syncytial Virus (RSV) is a common and highly contagious viral infection affecting the lungs and breathing passages. Because Tdap targets bacteria and RSV is a virus, the Tdap vaccine does not offer any protection against RSV disease in newborns. The protection conferred by the Tdap immunization is specific only to the bacterial diseases it targets.
Tdap’s Primary Role in Protecting Newborns
The primary reason a pregnant person receives the Tdap vaccine is to protect their newborn from pertussis, commonly known as whooping cough. Pertussis is a highly contagious bacterial infection that can be life-threatening for infants too young to start their own vaccination series. The Tdap shot is recommended during the third trimester of every pregnancy, ideally between 27 and 36 weeks of gestation.
This timing allows the pregnant person’s immune system to produce protective antibodies. These antibodies are actively transferred across the placenta to the developing fetus, providing temporary passive immunity. This transferred immunity guards the baby through the first couple of months of life, when they are most vulnerable to severe pertussis infection. The Tdap vaccine targets the bacteria responsible for pertussis, diphtheria, and tetanus.
The maternal Tdap vaccine is effective, potentially protecting more than three out of four babies from contracting whooping cough in their first two months of life. This strategy ensures the infant is born with a defense against a serious bacterial disease before they are old enough to receive the DTaP vaccine series themselves. Maternal transfer of antibodies is the most reliable method for protecting infants against severe pertussis disease.
Understanding Respiratory Syncytial Virus and Infant Vulnerability
Respiratory Syncytial Virus is a common seasonal virus that infects nearly all children by the time they reach two years of age. While it typically causes mild, cold-like symptoms in older children and adults, RSV is the leading cause of hospitalization for infants in the United States. The virus poses a significant threat to babies under six months because their small airways easily clog with mucus and inflammation.
RSV infection can progress to serious lower respiratory tract illnesses such as bronchiolitis (inflammation of the small airways) or pneumonia (an infection of the lungs). Symptoms in very young infants may include irritability, decreased activity, reduced feeding, and apnea (pauses in breathing). Because RSV is a virus, the Tdap vaccine does not produce the specific antibodies needed to neutralize the viral particles of RSV. A targeted approach is necessary for RSV prevention.
Targeted Prevention Strategies for RSV
Since the Tdap vaccine does not protect against RSV, two specific interventions have been developed to protect infants from severe RSV disease. These methods provide the targeted immunity that the Tdap vaccine cannot offer. One strategy is the administration of a maternal RSV vaccine, such as Abrysvo, given to the pregnant person during the third trimester, typically between 32 and 36 weeks gestation. This maternal vaccination works similarly to Tdap, prompting the production and transfer of RSV-specific antibodies across the placenta to the fetus.
The maternal RSV vaccine protects the newborn for the first few months after birth, with studies showing a reduction in the risk of severe RSV-associated lower respiratory tract disease by over 80%. The second strategy involves long-acting monoclonal antibodies, such as nirsevimab (marketed as Beyfortus). These are not vaccines but are ready-made antibodies administered directly to the infant as a single injection before or during their first RSV season.
Nirsevimab provides immediate, temporary passive protection by directly introducing the antibodies needed to fight the virus. It is recommended for all infants under eight months who are entering the RSV season. Most infants receive protection through either the maternal vaccine or the monoclonal antibody injection, but not both, as the goal is to ensure protection from severe disease with a single preventative measure. These targeted prevention tools offer high effectiveness against the leading cause of infant hospitalization.