Flu Vaccine
Everyday exposureVaccinesFluzone, FluMist
Also called · 7 names▾▴
flu shot, influenza vaccine, seasonal flu shot, flu jab, influenza shot, nasal flu vaccine, FluMist
Seasonal influenza vaccine
General information · effects depend on amount, timing, and how it is used. About these sources
Research strength: 4 / 5
CDC's September 1, 2026 page says its July 2025 seasonal schedule remains in effect for 2026-27 because of legal uncertainties and inquiries. CDC says pregnant people should receive an inactivated or recombinant vaccine, not the live nasal vaccine, and vaccination may occur in any trimester. For people in the first or second trimester in July or August, CDC prefers September or October unless a later visit may not be possible. Wu et al.'s 2026 review of 31 studies found no higher chance of total or major birth defects after first-trimester vaccination; it searched studies through April 2023 and included live births only. ACOG, SMFM, and AAP also recommend vaccination during pregnancy; UKHSA says inactivated vaccine should be offered regardless of stage from September 1, 2026. Ask your provider about your situation.
Last reviewed: 2026-10-14
Sources
- CDC: Interim Clinical Considerations for Seasonal Influenza VaccinesUS government
- ACOG: Influenza in Pregnancy, Prevention and TreatmentProfessional society
- Wu et al. 2026: First-trimester vaccination and birth defectsUS government
- Kharbanda et al. 2017: First-trimester influenza vaccinationUS government
- UKHSA: Vaccine Update, Flu Special 2026UK government
Research strength: 4 / 5
CDC says pregnant people should receive an inactivated or recombinant vaccine in any trimester, but not the live nasal vaccine. For people in the first or second trimester, CDC prefers September or October and says July or August vaccination should be avoided unless later vaccination may not be possible. Nordin et al. (2014) matched 57,554 vaccinated and unvaccinated pregnant women and found no higher chance of preterm birth or infants smaller than expected for pregnancy length. ACOG, SMFM, and AAP also recommend vaccination during pregnancy; UKHSA says pregnant women should be offered inactivated vaccine regardless of stage from September 1, 2026. Ask your provider about your situation.
Last reviewed: 2026-10-14
Sources
- CDC: Interim Clinical Considerations for Seasonal Influenza VaccinesUS government
- ACOG: Influenza in Pregnancy, Prevention and TreatmentProfessional society
- Nordin et al. 2014: Preterm and small-for-gestational-age outcomesUS government
- MotherToBaby: Seasonal Influenza VaccineTeratology service
- UKHSA: National Flu Programme 2026-27 LetterUK government
Research strength: 4 / 5
CDC says pregnant people should receive an inactivated or recombinant vaccine in any trimester, not the live nasal vaccine. CDC says July or August vaccination can be considered for people in the third trimester during those months because maternal vaccination has been linked with less infant flu illness in the first months after birth. Homaira et al. (2026) studied 147,907 matched infant pairs and estimated 21% vaccine effectiveness against infant flu notifications or hospitalizations in the first six months (95% CI 10-31); they found no significant effect on all-cause lower respiratory infection hospitalizations. ACOG and SMFM also recommend vaccination during pregnancy; UKHSA starts its inactivated-vaccine offer on September 1 regardless of pregnancy stage. Ask your provider about your situation.
Last reviewed: 2026-10-14
Sources
- CDC: Interim Clinical Considerations for Seasonal Influenza VaccinesUS government
- Homaira et al. 2026: Maternal vaccine effectiveness in infantsUS government
- ACOG: Influenza in Pregnancy, Prevention and TreatmentProfessional society
- SMFM: Respiratory Disease Season 2026-27Professional society
- UKHSA: National Flu Programme 2026-27 LetterUK government
Flu Vaccine — Breastfeeding
Research strength: 4 / 5
MotherToBaby and LactMed say breastfeeding is not a reason to avoid the injected or live nasal influenza vaccine. In Brady et al.'s 2018 trial of 248 nursing women, no influenza virus was detected in milk; one infant's nasal swab in the live-vaccine group showed a vaccine strain, but the infant was well and the authors could not rule out a sample mix-up. No independent confirmation of that one nasal finding was located. LactMed says antibodies in milk may add protection, but the clinical effect of milk alone is not known. CDC says the live nasal vaccine should not be used during pregnancy but can be used postpartum. Ask your provider about your situation.
Last reviewed: 2026-10-14
Sources
Pregnancy
Evidence is strongest for inactivated influenza vaccine (IIV); guidance also includes recombinant vaccine (RIV). Kharbanda et al. (2017) compared 52,856 first-trimester IIV-exposed singleton live births with 373,088 unexposed live births. Selected major structural defects occurred in 1.6 versus 1.5 per 100 live births, adjusted prevalence ratio 1.02 (95% CI 0.94-1.10). Nordin et al. (2014) matched 57,554 vaccinated and unvaccinated pregnant women, including 16,240 first-trimester pregnancies; it found no increased risk of preterm or small-for-gestational-age birth. Wu et al. (2026) pooled 31 studies with 1,223,024 participants. For first-trimester vaccination, adjusted OR was 1.03 (95% CI 0.98-1.07) for total birth defects and 1.03 (95% CI 0.98-1.09) for major defects. The review searched only through April 28, 2023 and included defects among live-born infants, not miscarriages or stillbirths. Tchuente et al. (2026) reported no significant association between vaccination and spontaneous abortion in a case-control group of 418 participants (aOR 0.53, 95% CI 0.10-2.68). The study used self-reported data collected in 2010-2012; the wide interval cannot rule out a modest effect. Hsiao et al. (2024) studied 48,781 pregnant people vaccinated with either recombinant RIV4 (14,981) or standard-dose IIV4 (33,800) and found no statistical difference in pregnancy, birth, or infant outcomes. The miscarriage comparison was 3.1% versus 3.0%, adjusted OR 0.95 (95% CI 0.85-1.05); this was a comparison between two vaccinated groups, not vaccinated versus unvaccinated. Sanofi sponsored the study and Sanofi employees were authors. FDA's July 2026 Flublok label describes a sponsor-owned registry of 14,981 pregnant individuals and reports no evidence of a vaccine-associated increase in major birth defects or miscarriage. The label notes that ectopic pregnancies and elective terminations were not collected. The registry and Hsiao cohort are not independent evidence against an unvaccinated group.
Breastfeeding
Schlaudecker et al. (2013) randomized 340 pregnant Bangladeshi women to influenza or pneumococcal vaccine; breast milk from 57 was analyzed. Influenza-specific milk IgA was higher in the influenza-vaccine group for at least six months. The study did not isolate milk-mediated protection from antibodies transferred through the placenta, and it was partly funded by Aventis Pasteur. Zaman et al. (2008) randomized 340 pregnant women; among their infants, laboratory-confirmed influenza occurred in 6 versus 16 cases, with estimated vaccine effectiveness of 63% (95% CI 5-85) through six months. This supports infant benefit after maternal vaccination, but does not show that milk alone caused the benefit. Brady et al. (2018) compared live attenuated nasal vaccine (LAIV) with IIV in 248 nursing women and 249 infants 28-120 days postpartum across two seasons. No vaccine or wild-type influenza virus was detected in milk, and IIV produced higher milk antibody responses on several measures. One infant in the LAIV group had vaccine strain detected in a nasal swab and remained asymptomatic; the authors could not determine whether mother and infant day-two samples were switched, so transmission was possible but not confirmed. Infants in the LAIV group had more irritability or fussiness than the IIV group (59.7% versus 44.8%, p=0.02). The trial had no primary safety hypothesis and was too small to rule out rare outcomes. It was NIH-funded, but authors disclosed manufacturer ties and MedImmune manuscript and assay involvement.
Seasonal influenza vaccines are not all the same formulation. CDC describes injected inactivated vaccines (IIV3), injected recombinant vaccines (RIV3), and a live attenuated nasal vaccine (LAIV3). Fluzone is an inactivated vaccine, Flublok is recombinant, and FluMist is live attenuated. CDC says pregnant women should receive IIV3 or RIV3, not LAIV3. Product composition is updated for each influenza season.
What was tested
Pregnancy studies include observational cohorts, case-control studies, and a systematic review of first-trimester vaccination. Outcomes include selected birth defects, miscarriage, preterm birth, small-for-gestational-age birth, stillbirth, and infant outcomes. Kharbanda 2017, Nordin 2014, Wu 2026, and Tchuente 2026 use different populations and outcome definitions; Wu's review includes live births only. Hsiao 2024 compares two vaccinated formulations and is Sanofi-sponsored. Breastfeeding evidence includes a trial of live nasal versus inactivated vaccine in nursing women, a pregnancy vaccine trial that measured breast milk antibodies, and a maternal-vaccination infant-outcome trial. These studies do not establish the clinical effect of milk alone.
2026-27 policy status and seasonal vaccination timing
- Source A says
- CDC's September 1, 2026 page says the July 2025 seasonal schedule remains in effect for 2026-27 because of legal uncertainties and inquiries. It recommends IIV3 or RIV3 in pregnancy, says LAIV3 should not be used during pregnancy, and gives trimester-specific July/August timing guidance. (CDC: Interim Clinical Considerations for Seasonal Influenza Vaccines)
- Source B says
- ACOG's advisory, last updated September 2026, recommends an inactivated or recombinant vaccine as soon as available for people who are or will be pregnant during influenza season. UKHSA says pregnant women should be offered inactivated vaccine regardless of pregnancy stage from September 1, 2026. (ACOG: Influenza in Pregnancy, Prevention and Treatment, UKHSA: Vaccine Update, Issue 375, Flu Special 2026, UKHSA: National Flu Programme 2026-27 Letter)
- Why they differ
- CDC provides trimester-specific timing and describes the US schedule's current legal status. ACOG provides clinical practice guidance, while UKHSA and the UK programme describe national timing and delivery. Their core recommendation is aligned on vaccination during pregnancy with an inactivated or recombinant vaccine; their timing language and programme context differ.
- Other sources
- SMFM recommends the updated 2026-27 seasonal inactivated or recombinant influenza vaccine during pregnancy. AAP recommends influenza vaccination in pregnancy and for breastfeeding parents. (SMFM: Respiratory Disease Season 2026-27, AAP: 2026-27 Influenza Prevention and Treatment Recommendations)
- What the evidence shows overall
- No substantive disagreement about pregnancy vaccination was found. Keep the compatible ratings and disclose the product and timing details. The timing preference is not evidence of established fetal harm.
- CDC says pregnant women should receive IIV3 or RIV3; LAIV3 should not be used during pregnancy but can be used postpartum. (CDC)
- ACOG recommends an inactivated or recombinant influenza vaccine as soon as it is available for people who are or will be pregnant during influenza season. (ACOG)
- UKHSA says all pregnant women, including those who become pregnant during the flu season, should be offered an inactivated influenza vaccine regardless of pregnancy stage. (UKHSA)
General research, not specific to pregnancy.
FDA's current Fluzone label describes a febrile-seizure signal in children 6 months through 4 years during the first day after standard-dose vaccination. This concerns children receiving the vaccine, not infants exposed only through a breastfeeding parent's vaccination.
- The Fluzone label reports increased febrile-seizure risk on the first day after standard-dose trivalent or quadrivalent influenza vaccination in children 6 months through 4 years. One data partner estimated 21.2 excess events per million quadrivalent doses and 44.2 per million trivalent doses. FDA's January 9, 2026 notice gives the same estimates; Lloyd et al. 2025 is the primary study. (DailyMed: Fluzone Prescribing Information, FDA: Fluzone Safety Label Change Notification, Lloyd et al. 2025: Influenza vaccine post-licensure surveillance)
- MotherToBaby: Seasonal Influenza Vaccine (Flu Shot)Teratology serviceSecondary
- LactMed: Influenza VaccinesUS governmentSecondaryPage dated 2026-05-15Independent check
- CDC: Guidelines for Vaccinating Pregnant WomenUS governmentSecondaryIndependent check
- CDC: Interim Clinical Considerations for Seasonal Influenza VaccinesUS governmentSecondaryPage dated 2026-09-01Independent check
- ACOG: Influenza in Pregnancy, Prevention and TreatmentProfessional societySecondaryIndependent check
- SMFM: Respiratory Disease Season 2026-27Professional societySecondaryIndependent check
- AAP: 2026-27 Influenza Prevention and Treatment RecommendationsSecondaryIndependent check
- UKHSA: Vaccine Update, Issue 375, Flu Special 2026UK governmentSecondaryPage dated 2026-09-08Independent check
- UKHSA: National Flu Programme 2026-27 LetterUK governmentSecondaryPage dated 2026-06-09Independent check
- Kharbanda et al. 2017: First-trimester influenza vaccination and birth defectsUS governmentPrimaryIndependent check
- Nordin et al. 2014: Preterm and small-for-gestational-age outcomesUS governmentPrimaryIndependent check
- Wu et al. 2026: First-trimester influenza vaccination and birth defectsUS governmentPrimaryIndependent check
- Tchuente et al. 2026: Maternal influenza vaccination and pregnancy outcomesUS governmentPrimaryIndependent check
- Hsiao et al. 2024: Recombinant versus standard-dose influenza vaccine during pregnancyUS governmentPrimary
- FDA: Flublok 2026-27 Prescribing InformationUS governmentTertiary
- FDA CBER: Real-World Evidence Label Change TableUS governmentSecondaryPage dated 2026-03-06
- Schlaudecker et al. 2013: Influenza antibodies in human milkUS governmentPrimary
- Zaman et al. 2008: Maternal influenza immunization and infant outcomesUS governmentPrimaryIndependent check
- Brady et al. 2018: Live versus inactivated vaccine in nursing womenUS governmentPrimary
- DailyMed: FluMist Prescribing InformationDrug company labelTertiaryPage dated 2026-07-28
- Homaira et al. 2026: Maternal influenza vaccination effectiveness in infantsUS governmentPrimary
- DailyMed: Fluzone Prescribing InformationDrug company labelTertiaryPage dated 2026-07-06
- FDA: Fluzone Safety Label Change NotificationUS governmentSecondaryPage dated 2026-01-09
- Lloyd et al. 2025: Influenza vaccine post-licensure surveillanceUS governmentPrimaryIndependent check
Last reviewed 2026-10-14
Independent check 2026-10-14
Not yet clinician-reviewed
Ask your provider about your situation.
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