The American College of Obstetricians and Gynecologists (ACOG) now recommends that eligible pregnant patients receive the maternal RSV vaccine from Sept. 1 through March 1, extending the previous end date of Jan. 31. The change is part of ACOG's 2026-27 respiratory virus season immunization guidance. The gestational age window did not change: a single dose of Pfizer's Abrysvo between 32 weeks 0 days and 36 weeks 6 days of pregnancy, for patients who do not have a delivery planned within two weeks.
ACOG says the extension reflects recent RSV seasons that have run later into the spring and become more severe. Under the old calendar, a patient who reached 32 weeks in February would have fallen outside the recommended window.
The guidance also shows how much room there is to improve. ACOG reports that 41.6% of eligible pregnant individuals have received the maternal RSV vaccine, which means most eligible patients have not.
A Five-Week Window Tied to the Due Date
Eligibility is narrow. The window opens at 32 weeks 0 days and closes at 36 weeks 6 days, a span of about five weeks.
Protection is not immediate. According to CDC guidance on protecting infants from RSV, it takes about two weeks after vaccination for the pregnant patient to develop antibodies and pass that protection to the baby. The protection lasts through about the first six months after birth, when babies are at highest risk of severe RSV.
Patients past 36 weeks 6 days are not candidates for the maternal vaccine. For them, and for anyone who declines it, the alternative is to protect the baby directly with a long-acting infant antibody, nirsevimab or clesrovimab. The CDC says the antibody should be given shortly before RSV season or, for babies born during the season, within one week after birth.
Both approaches have shown real-world benefit. According to ACOG's guidance, maternal vaccination reduced the risk of infant hospitalization by 51% to 70%, while nirsevimab reduced RSV-related hospitalization by 63.6% to 93% during the first RSV season.
One rule often surprises patients who have been pregnant before. The maternal vaccine is given only once. ACOG says there are no data on its effectiveness in later pregnancies, and the CDC does not currently recommend another dose. Babies born after a later pregnancy should receive an infant antibody instead.
ACOG and CDC Now List Different End Dates
Families comparing documents will see two end dates. The CDC's page for parents still describes maternal vaccination from September through January in most of the United States, while ACOG now says Sept. 1 through March 1. Both are current published guidance, and the difference is not a typo.
As a result, access may depend on which schedule a practice follows and what a clinic or pharmacy has in stock. A patient who reaches 32 weeks in February should ask her clinician which calendar the practice uses rather than assume the later date applies everywhere.
Insurance is worth raising in the same conversation, because coverage rules may follow federal recommendations rather than professional society guidance. Patients covered by Medicaid or treated at community health centers should ask what is available on-site. For infants, the CDC says nirsevimab is covered through the federal Vaccines for Children program, which serves children who are Medicaid-eligible, uninsured, underinsured, or American Indian or Alaska Native.
Clinicians Describe It as Routine Care
ACOG President Camille A. Clare, MD, MPH, tied the guidance to preventable complications. "Vaccination is standard preventive care," she said in the college's announcement, adding that some complications in pregnancy that result from not being vaccinated are completely preventable.
Kevin Ault, MD, a co-author of the guidance, told Contemporary OB/GYN that accumulating real-world evidence continues to mirror the results of the phase 3 clinical trials.
MedicalDaily previously reported on two ways families can shield a newborn from RSV and on the WHO clearance of a multi-dose maternal RSV vial. What is new is the extended eligibility window and an uptake figure showing that most eligible patients remain unvaccinated.
The CDC lists common side effects of the maternal vaccine as headache, nausea, and pain at the injection site. It lists hypertensive disorders of pregnancy, including preeclampsia, as a possible risk under further study. That is a topic to discuss at a prenatal visit, not a reason to skip the conversation.
Questions for the Next Prenatal Visit
Patients between 32 and 36 weeks should ask whether they are eligible now, whether the practice stocks the vaccine on-site, and what the plan is if delivery comes early. Under CDC clinical guidance, babies born less than two weeks after maternal vaccination are generally advised to receive an infant antibody as well.
Patients past the window, or those who received the vaccine in an earlier pregnancy, should ask which infant antibody the birth hospital uses and when it would be given.
Parents should seek urgent medical care if a baby has trouble breathing, fast or labored breathing, poor feeding, fewer wet diapers, or bluish coloring around the lips. These signs can distinguish severe RSV from an ordinary cold.
Several questions remain open: whether federal guidance will adopt the March 1 end date, how much of the vaccination gap reflects access problems rather than personal choice, and whether the 2026-27 season will again run late. MedicalDaily will report any CDC change to the seasonal window and any new effectiveness data.
Key Questions Answered
What changed in the guidance?
ACOG extended the maternal RSV vaccination period from a Jan. 31 end date to March 1, because recent RSV seasons have run later into the spring and become more severe.
Who is eligible now?
Pregnant patients between 32 weeks 0 days and 36 weeks 6 days of gestation who do not have a delivery planned within two weeks and who did not receive the maternal RSV vaccine in a previous pregnancy.
How soon does it protect the baby?
It takes about two weeks for antibodies to develop and pass to the baby. Protection lasts through about the first six months after birth.
What if someone is past 36 weeks and 6 days?
The maternal vaccine is not recommended at that point. The baby can receive a long-acting infant antibody instead, a decision to make with a clinician.
Do babies need both the vaccine and the antibody?
Most do not. One option is generally enough, though babies born less than two weeks after maternal vaccination are generally advised to receive the antibody as well.
Why do CDC and ACOG list different end dates?
The CDC's parent page still describes September through January, while ACOG has extended eligibility to March 1. Patients should confirm which schedule their practice follows.
Where can families get these products at low cost?
Nirsevimab is covered through the federal Vaccines for Children program for eligible children. Patients should ask their clinic or county health department what is in stock and what their plan covers.
