Receive an inactivated influenza vaccine during pregnancy if pregnant during flu season; it can be administered at any gestational stage, but avoid live-attenuated nasal sprays

Pregnant women face significantly higher risks of hospitalization from influenza than non-pregnant individuals. Receiving a flu shot during pregnancy reduces the mother's risk of flu-related hospitalization by roughly 40%. It also cuts laboratory-confirmed influenza in infants during their first 6 months of life by approximately half, and cuts infant flu hospitalizations by roughly 70%. Evidence shows no increase in miscarriage, stillbirth, or congenital anomalies.

Out of pocket, a flu vaccine costs a few tens of dollars; requires one visit to a community vaccination clinic. The only friction is selecting a brand whose product leaflet does not list pregnancy as an absolute contraindication.

The World Health Organization (WHO) 2022 influenza position paper highlights that pregnant women have an odds ratio of 6.8 (95% CI 6.0–7.7) for flu-related hospitalization compared to non-pregnant peers. A randomized controlled trial in Bangladesh enrolled 340 pregnant women assigned to inactivated influenza vaccine or pneumococcal control, followed through 24 weeks postpartum: vaccine efficacy against laboratory-confirmed influenza in infants was 63% (95% CI 5%–85%), while maternal febrile respiratory illness was reduced by 36% (95% CI 4%–57%). In double-blind placebo-controlled trials in South Africa, maternal vaccination reduced confirmed influenza by 50.4% in mothers and 48.8% in infants. A meta-analysis pooling four trials and three observational cohorts demonstrated that maternal vaccination reduced infant laboratory-confirmed influenza in the first 6 months of life by 48% (95% CI 33%–59%) and infant influenza hospitalizations by 72% (95% CI 39%–87%). A multi-country retrospective study across four nations (2010–2016) demonstrated a 40% reduction (95% CI 12%–59%) in maternal laboratory-confirmed influenza hospitalizations. In terms of safety, a systematic review of 40 studies found no excess risk of stillbirth (aOR 0.84, 95% CI 0.65–1.08) or congenital malformations (aOR 1.03, 95% CI 0.99–1.07), while preterm birth was reduced by 13% (aOR 0.87, 95% CI 0.78–0.96). A US Vaccine Safety Datalink study of three influenza seasons (2012–2015) found no association between vaccination in the preceding 28 days and spontaneous abortion (aOR 0.9, 95% CI 0.6–1.5). The Chinese Center for Disease Control and Prevention (China CDC) Technical Guidelines prioritize pregnant women for seasonal vaccination at any gestational stage, noting third-trimester vaccination provides optimal passive transplacental antibodies to neonates.

Controversy: A 2017 US study reported an association between first-trimester flu vaccination and spontaneous abortion within 28 days among women also vaccinated with pH1N1 in the prior season (aOR 2.0, 95% CI 1.1–3.6); however, the authors noted potential confounding, and subsequent larger investigations across three subsequent seasons failed to replicate this association. Live attenuated influenza vaccine (LAIV nasal spray) is strictly contraindicated in pregnancy; only injectable inactivated influenza vaccines should be administered. Because infants younger than 6 months cannot receive flu vaccination directly, maternal vaccination constitutes their primary antibody defense against winter influenza. For adult routine flu vaccination evidence, see Chapter 1, Rule 20.

World Health Organization (2022). Vaccines against influenza: WHO position paper – May 2022. Weekly Epidemiological Record, 97(19), 185-208. https://iris.who.int/server/api/core/bitstreams/420b8e49-9f16-461d-a5d8-263069778432/content；Zaman K, Roy E, Arifeen SE, et al. (2008). Effectiveness of maternal influenza immunization in mothers and infants. New England Journal of Medicine, 359(15), 1555-1564. https://doi.org/10.1056/NEJMoa0708630；Madhi SA, Cutland CL, Kuwanda L, et al. (2014). Influenza vaccination of pregnant women and protection of their infants. New England Journal of Medicine, 371(10), 918-931. https://doi.org/10.1056/NEJMoa1401480；Nunes MC, Madhi SA (2018). Influenza vaccination during pregnancy for prevention of influenza confirmed illness in the infants: A systematic review and meta-analysis. Human Vaccines & Immunotherapeutics, 14(3), 758-766. https://doi.org/10.1080/21645515.2017.1345385；Jarvis JR, Dorey RB, Warricker FDM, Alwan NA, Jones CE (2020). The effectiveness of influenza vaccination in pregnancy in relation to child health outcomes: Systematic review and meta-analysis. Vaccine, 38(7), 1601-1613. https://doi.org/10.1016/j.vaccine.2019.12.056；Thompson MG, Kwong JC, Regan AK, et al. (2019). Influenza Vaccine Effectiveness in Preventing Influenza-associated Hospitalizations During Pregnancy: A Multi-country Retrospective Test Negative Design Study, 2010-2016. Clinical Infectious Diseases, 68(9), 1444-1453. https://doi.org/10.1093/cid/ciy737；Giles ML, Krishnaswamy S, Macartney K, Cheng A (2019). The safety of inactivated influenza vaccines in pregnancy for birth outcomes: a systematic review. Human Vaccines & Immunotherapeutics, 15(3), 687-699. https://doi.org/10.1080/21645515.2018.1540807；Donahue JG, Kieke BA, King JP, et al. (2019). Inactivated influenza vaccine and spontaneous abortion in the Vaccine Safety Datalink in 2012-13, 2013-14, and 2014-15. Vaccine, 37(44), 6673-6681. https://doi.org/10.1016/j.vaccine.2019.09.035；Donahue JG, Kieke BA, King JP, et al. (2017). Association of spontaneous abortion with receipt of inactivated influenza vaccine containing H1N1pdm09 in 2010-11 and 2011-12. Vaccine, 35(40), 5314-5322. https://doi.org/10.1016/j.vaccine.2017.06.069（备注里的反方研究）；中国疾病预防控制中心 (2026). 中国流感疫苗预防接种技术指南（2026—2027）. https://www.chinacdc.cn/jkyj/mygh02/jswj2026/202609/t20260902_1839739.html