The stretch between birth and a baby's first vaccinations is the period when several common infections do their worst damage, and the only immune protection available during those weeks is what crossed the placenta before delivery. That biology is why obstetric groups recommend specific vaccines during pregnancy rather than after.
The timing gap is concrete. Infants do not begin their own pertussis vaccine series until around two months of age, and most pertussis deaths occur in babies younger than three months. Influenza vaccination cannot begin until six months. RSV season arrives regardless of how old a baby is when it starts.
With the RSV vaccination window for pregnancy opening in September, expectant families face practical questions now about which vaccines apply, when, and what protection a newborn actually receives.
The Transfer Mechanism That Makes Timing Matter
Antibodies do not cross the placenta at a constant rate. Transfer of maternal immunoglobulin G accelerates substantially in the third trimester, which is why recommendations specify gestational windows rather than telling patients to get vaccinated whenever convenient.
For Tdap, guidance calls for a dose during each pregnancy regardless of prior Tdap history, preferably during the early part of gestational weeks 27 through 36. Vaccinating earlier within that window gives the pregnant patient time to mount her own antibody response before those antibodies are handed across.
Each pregnancy instruction surprises many parents. Antibody levels wane, and a dose given during a previous pregnancy does not protect the next baby.
For RSV, CDC guidance for pregnant women recommends a single dose of the maternal vaccine Abrysvo between 32 weeks 0 days and 36 weeks 6 days of gestation, administered seasonally from September through January in most of the United States. Patients past 36 weeks 6 days should not be vaccinated, because there is unlikely to be enough time for antibodies to develop and cross the placenta.
Influenza vaccine can be given in any trimester, and only inactivated or recombinant formulations are used during pregnancy.
Two Products, One Decision, for RSV Protection
RSV is the area where families most often get confused, because there are two ways to protect a baby, and most infants need only one.
The first is maternal vaccination during the 32- to 36-week window. The second is an infant monoclonal antibody, nirsevimab or clesrovimab, given directly to the baby. CDC recommends the infant antibody when the birthing parent was not vaccinated during the current pregnancy, timed just before or at the start of RSV season.
The rule for subsequent pregnancies is specific. The maternal vaccine is a one-time dose given during a patient's first eligible pregnancy, and repeat vaccination is not indicated in later pregnancies. Those infants should receive the monoclonal antibody instead. Discussing both options and the patient's preference is part of the recommended conversation, not an afterthought.
MedicalDaily previously reported on research findings showing that maternal RSV vaccination is associated with substantial protection against hospitalization in infants younger than three months in a western Pennsylvania study. A separate large analysis linked the infant antibody to fewer serious bacterial infections, a finding MedicalDaily covered that could not be extended to the maternal vaccine because that product was not included in the analysis.
The Guidance Split Patients Are Encountering
Expectant parents may receive different answers from different clinicians this year, and it helps to know why rather than assuming someone is misinformed.
The American College of Obstetricians and Gynecologists released its own 2026 maternal immunization schedule in June, endorsed by 13 medical and health organizations, including the American Academy of Pediatrics, the American Academy of Family Physicians, and the Society for Maternal-Fetal Medicine. It followed ACOG's withdrawal in February as a liaison organization to the CDC's Advisory Committee on Immunization Practices, a decision ACOG attributed to concerns about the committee's scientific integrity.
The ACOG schedule lists influenza, COVID-19, Tdap, and RSV vaccines as routinely recommended during pregnancy and marks the first time the organization has issued recommendations that differ from federal guidance. The COVID-19 recommendation is the primary point of divergence, since current CDC guidance no longer recommends the vaccine for healthy pregnant women.
For a patient, the practical consequence is that an obstetric practice and a retail pharmacy may be working from different documents. That is a reason to ask which schedule a clinician follows rather than a reason to skip the conversation.
Scientific consensus on the other maternal vaccines is not in dispute among obstetric and pediatric organizations. The disagreement concerns one product and the process that produced federal recommendations, not whether antibody transfer protects newborns.
Preparing for the Conversation at a Prenatal Visit
Patients due in late fall or winter should raise RSV timing at their next visit if they have not already, since the window closes at 36 weeks 6 days and a missed appointment can close it entirely.
Useful questions include which vaccines are recommended at the current gestational age, whether a previous pregnancy's RSV vaccine means the baby should get the monoclonal antibody instead, whether the practice administers vaccines on-site or refers to a pharmacy, and what each will cost under the patient's plan. Most insurance plans cover recommended maternal immunizations without cost-sharing, and Medicaid programs cover them, but confirming helps avoid a surprise bill.
Families should also ask about vaccination for other adults in the household. Adults are a common source of pertussis infection in newborns, and vaccinating close contacts is a longstanding complement to maternal immunization.
Patients with questions about vaccine safety during pregnancy deserve a direct answer from their own clinician rather than a search result. Anyone with an immune condition, a history of a vaccine reaction, or a complicated pregnancy should discuss individual circumstances with their obstetric provider. This article is general information and is not medical advice.
CDC updates its RSV immunization guidance as products and seasonality data change, and jurisdictions with different seasonal patterns, including Alaska, Hawaii, Puerto Rico, and several U.S. territories, follow state, local, or territorial guidance instead. MedicalDaily will report on changes to federal or professional society recommendations ahead of the coming respiratory season.
Key Questions Answered
Why are vaccines given during pregnancy rather than to the newborn? Infants cannot begin their own pertussis series until around two months and influenza vaccination until six months. Antibodies transferred across the placenta cover that gap.
Which vaccines are recommended during pregnancy? Influenza in any trimester using inactivated or recombinant formulations, Tdap during each pregnancy preferably early in gestational weeks 27 through 36, and the RSV vaccine between 32 weeks 0 days and 36 weeks 6 days seasonally. ACOG also recommends COVID-19 vaccination.
Why is Tdap repeated in every pregnancy? Antibody levels wane over time, so a dose from a previous pregnancy does not provide the same protection to a subsequent baby.
Does the baby need the RSV antibody too? Usually not if the birthing parent received the RSV vaccine during that pregnancy. CDC recommends the infant monoclonal antibody when the parent was not vaccinated during the current pregnancy, including in later pregnancies where repeat maternal vaccination is not indicated.
Why are ACOG and CDC guidance different? ACOG released its own 2026 maternal immunization schedule after withdrawing as a liaison to the CDC advisory committee. The main difference is that ACOG continues to recommend COVID-19 vaccination during pregnancy.
How long does the protection last? RSV antibodies transferred during pregnancy are intended to cover the infant's first RSV season, and protection wanes over time. Pertussis and influenza protection covers the early months before infant vaccination begins.
Should other family members be vaccinated? Adults are a common source of pertussis infection in newborns, and vaccinating close household contacts is a longstanding complement to maternal immunization.
