Skip to Content
Canadian Paediatric Society

Practice Point

The benefits of influenza vaccine in pregnancy for the fetus and the infant younger than six months of age

Posted: Nov 3 2014 | Updated: Jul 23 2018

The Canadian Paediatric Society gives permission to print single copies of this document from our website. For permission to reprint or reproduce multiple copies, please see our copyright policy.

Principal author(s)

Noni E MacDonald, Jane C McDonald; Canadian Paediatric Society, Infectious Diseases and Immunization Committee


Influenza is a serious problem for infants <6 months of age, whose hospitalization rates for influenza and associated illness are comparable with rates in the elderly. Because influenza vaccines are not effective in this age group, the optimal evidence-based strategy is to administer trivalent inactivated influenza vaccines during pregnancy. Immunizing with trivalent inactivated influenza vaccines in the second and third trimester is well studied and safe, not only providing protection for the pregnant woman and her infant <6 months of age, but also for the fetus by decreasing the risk for low birth weight.

Key Words: ALRI; Cocooning; Influenza; TIV

The global influenza disease burden in children <5 years of age is substantial, with an estimated 90 million cases in 2008, 20 million with acute lower respiratory illness and 28,000 to 111,500 deaths.[1] Even in industrialized countries, influenza remains a significant cause of hospitalization, emergency room visits and outpatient visits in this age group. Infants <6 months of age have the highest rate of influenza-attributable hospitalizations in any paediatric age group,[2]with estimates that range from nine to 104 per 10,000 infants <6 months of age,[3]comparable with rates observed in adults >80 years of age.

For infants and children ≥6 months of age, the trivalent inactivated influenza vaccines (TIV) have been shown to be a safe and effective means of decreasing risk for severe illness with influenza.[4][5] However, preventing influenza in children at highest risk for severe disease, particularly infants <6 month of age, is more problematic. Beyond practicing meticulous hand hygiene during influenza season and avoiding contact with infected people, different immunization strategies have been assessed.

Influenza vaccines are not licensed or recommended for infants <6 months of age[4] because their immune response, when studied, has been variable and vaccine effectiveness is unclear.[6]  Two other immunization strategies to protect the very young have been evaluated: ‘cocooning’ (the immunization of postpartum women and an infant’s household contacts); and immunizing pregnant women.

Cocooning programs have met with some success and evidence suggests that the maternal immunization component provides most of an infant’s protection from influenza.[7] However, while the strategy works moderately well in research studies and some clinical settings, the programs are costly and have proven difficult to implement on a large scale.[8] Furthermore, they are not cost effective in preventing pertussis deaths in infants <6 months of age,[9] and are, therefore, unlikely to be cost effective in preventing influenza deaths in same age group.

By contrast, the strategy of immunizing pregnant women during their second or third trimester has been shown in both randomized controlled trials and in population studies to be clinically effective,[10]-[13]safe[11]-[22] and cost effective, with decreased hospitalization rates for both mothers and young infants during influenza season.[13][23]-[26] Beyond lower maternal and infant influenza-related hospitalization rates, a review of studies investigating antenatal influenza immunization in the second and third trimester, including Canadian studies, has shown reduced frequencies of both preterm and small-for-gestational age (growth-restricted) newborns, albeit with wide variation in effect.[13][27]-[32] Within this group of studies, two were conducted in Canada. One Nova Scotia study showed an adjusted OR of 0.75 (95% CI 0.60 to 0.94) for a reduced risk of preterm delivery (<37 weeks) and an adjusted OR 0.96 (95% CI 0.79 to 1.16) for reduced risk of SGA (<10 percentile).[28] The larger study, done in Ontario, specifically showed a reduction in the risk of preterm delivery (<32 weeks) with an adjusted RR of 0.73 (95% CI 0.58 to 0.91) and a reduction in the risk for SGA (<3 percentile) adjusted RR of 0.81 (95% CI 0.72 to 0.92).[29] Furthermore, infant immunization with conjugated pneumococcal vaccine is more effective in preventing otitis media after maternal infleunza vaccine in pregnancy.[33].

Influenza immunization in early pregnancy may be of even greater value. A 2014 systematic review and meta-analysis of the impact of influenza in the first trimester showed higher risk for congenital anomalies, notably neural tube defects, hydrocephaly, congenital heart defects (eg, aortic valve atresia or stenosis and ventricular septal defect), as well as cleft lip, and digestive system and limb reduction defects.[34] Such teratogenic effects may be a consequence of fever and/or other host responses to influenza infection. Potentially, first-trimester influenza immunization could avert some congenital anomalies. The National Advisory Committee on Immunization recommends immunization with TIV for women in any stage of pregnancy.[35] This recommendation is supported by the Society of Obstetricians and Gynecologists of Canada: However, because uptake is far from universal, greater efforts are needed both to encourage health care workers to offer influenza vaccine to pregnant women and for women to accept. If the vaccine was not given during pregnancy, mothers of young infants should be immunized to decrease the risk for influenza and, if breastfeeding, the infant receives further protection from the passive transfer of antibodies in breast milk.[36]

In summary, to prevent influenza in infants <6 months of age, the best evidence-based strategy is to administer influenza vaccines during pregnancy. Immunization with TIV in the second and third trimester is well studied, safe and has protective effects for both mother and child before birth. Furthermore, the infant is born with influenza antibodies, which offer some protection until the first dose of influenza vaccine can be given at six months of age. In temperate climates where influenza is seasonal, maternal immunization should be performed before influenza season starts. While appropriate hand hygiene by everyone in contact with infants during influenza season and avoiding contact between infants and infected people can help to prevent illness, immunization in pregnancy is a key step to protecting an especially vulnerable group in their first months of life.


This practice point was reviewed by the Fetus and Newborn Committee of the Canadian Paediatric Society, as well as by representatives from the Society of Obstetricians and Gynecologists of Canada and the College of Family Physicians of Canada.

Members: Natalie A Bridger MD; Jane C Finlay MD (past member); Susanna Martin MD (Board Representative); Jane C McDonald MD; Heather Onyett MD; Joan L Robinson MD (Chair); Marina I Salvadori MD (past member); Otto G Vanderkooi MD
Liaisons: Upton D Allen MBBS, Canadian Pediatric AIDS Research Group; Michael Brady MD, Committee on Infectious Diseases, American Academy of Pediatrics; Charles PS Hui MD, Committee to Advise on Tropical Medicine and Travel (CATMAT), Public Health Agency of Canada; Nicole Le Saux MD, Immunization Monitoring Program, ACTive (IMPACT); Dorothy L Moore MD, National Advisory Committee on Immunization (NACI); Nancy Scott-Thomas MD, College of Family Physicians of Canada; John S Spika MD, Public Health Agency of Canada
Consultant: Noni E MacDonald MD
Principal authors: Noni E MacDonald MD, Jane C McDonald MD


  1. Nair H, Brooks WA, Katz M, et al. Global burden of respiratory infections due to seasonal influenza in young children: A systematic review and meta-analysis. Lancet 2011;378(9807):1917-30.
  2. Neuzil KM, Mellen BG, Wright PF, Mitchel EF Jr, Griffin MR. The effect of influenza on hospitalizations, outpatient visits and courses of antibiotics in children. N Engl J Med 2000;342(4):225-31.
  3. Poehling KA, Edwards KM, Griffin MR, et al. The burden of influenza in young children, 2004-2009. Pediatrics 2013;131(2):207-16.
  4. Public Health Agency of Canada, National Advisory Committee on Immunization (NACI). Statement on seasonal influenza vaccine for 2013-14. Canada Communicable Disease Report CCDR. October 2013; 39(ACS-4): (Accessed October 6, 2014).
  5. SAGE Working Group. Background paper on influenza vaccines and immunization: (Accessed October 6, 2014).
  6. Walter EB, Englund JA, Blatter M, et al; GRC27 Study Team. Trivalent inactivated influenza virus vaccine given to two-month-old children: An off-season pilot study. Pediatr Infect Dis J 2009;28(12):1099-104.
  7. Maltezou HC, Fotiou A, Antonakopoulos N, et al. Impact of postpartum influenza vaccination of mothers and household contacts in preventing febrile episodes, influenza-like illness, healthcare seeking, and administration of antibiotics in young infants during the 2012-2013 influenza season. Clin Infect Dis 2013;57(11):1520-6.
  8. Guzman-Cottrill JA, Phillipi CA, Dolan SA, Nyquist AC, Win A, Siegel J. Free vaccine programs to cocoon high-risk infants and children against influenza and pertussis. Am J Infect Control 2012;40(9):872-6.
  9. Skowronski DM, Janjua NZ, Tsafack EP, Ouakki M, Hoang L, De Serres G. The number needed to vaccinate to prevent infant pertussis hospitalization and death through parent cocoon immunization. Clin Infect Dis 2012;54(3):318-27.
  10. Steinhoff MC, Omer SB. A review of fetal and infant protection associated with antenatal influenza immunization. Am J Obstet Gynecol 2012;207(3 Suppl):S21-7.
  11. Madhi SA, Cutland CL, Kuwanda L, et al; Maternal Flu Trial (Matflu) Team. Influenza vaccination of pregnant women and protection of their infants. N Engl J Med 2014;371(10):918-31.
  12. Håberg SE, Trogstad L, Gunnes N et al. Risk of fetal death after pandemic influenza virus infection or vaccination. N Eng J Med 2013;368(4):333-40.
  13. Omer SB. Maternal immunization. N Engl J Med 2017;376(25):1256-67.
  14. Tamma PD, Ault KA, del Rio C, Steinhoff MC, Halsey NA, Omer SB. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol 2009;201(6):547-52.
  15. Ludvigsson JF, Ström P, Lundholm C et al. Maternal vaccination against H1N1 influenza and offspring mortality: Population based cohort study and sibling design. BMJ 2015;351:h5585.
  16. Omon E, Damase-Michel C, Hurault-Delarue C et al. Non-adjuvanted 2009 influenza A (H1N1)v vaccine in pregnant women: The results of a French prospective descriptive study. Vaccine 2011;95(52):9649-54.
  17. Munoz FM, Greisinger AJ, Wehmanen OA et al. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol 2005;192(4):1098-106.
  18. Moro PL. Broder K, Zheteyeva Y et al. Adverse events following administration to pregnant women of influenza A (H1N1) 2009 monovalent vaccine reported to the Vaccine Adverse Event Reporting System. Am J Obstet Gynecol 2011;205(5):473.e1-9.
  19. Moro PL, Museru OI, Broder K et al. Safety of influenza A (H1N1) 2009 live attenuated monovalent vaccine in pregnant women. Obstet Gynecol 2013;122(6):1271-8.
  20. Tavares F, Nazareth I, Monegal JS, Kolte I, Verstraeten T, Bauchau V. Pregnancy and safety outcomes in women vaccinated with an ASO3-adjuvanted split virion H1N1 (2009) pandemic influenza vaccine during pregnancy: A prospective cohort study. Vaccine 2011;29(37):6358-65.
  21. Rubinstein F, Micone P, Bonotti A et al. Influenza A/H1N1 MF59 adjuvanted vaccine in pregnant women and adverse perinatal outcomes: Multicentre study. BMJ 2013;346:f393.
  22. Kharbanda EO, Vazquez-Benitez G, Lipkind H et al. Inactivated influenza vaccine during pregnancy and risks for adverse obstetric events. Obstet Gynecol 2013;122(3):659-67.
  23. Beigi RH, Wiringa AE, Bailey RR, Assi TM, Lee BY. Economic value of seasonal and pandemic influenza vaccination during pregnancy. Clin Infect Dis 2009;49(12):1784-92.
  24. Skedgel C, Langley JM, MacDonald NE, Scott J, McNeil S. An incremental economic evaluation of targeted and universal influenza vaccination in pregnant women. Can J Public Health 2011;102(6):445-50.
  25. Benowitz I, Esposito DB, Gracey KD, Shapiro EF, Vásquez M. Influenza vaccine given to pregnant women reduces hospitalizations due to influenza in their infants. Clin Infect Dis 2010;51(12):1355-61.
  26. Eick AA, Uyeki TM, Klimov A et al. Maternal influenza vaccination and effect on influenza virus infection in young infants. Arch Pediatrics Adolesc Med 2011;165(2):104-11.
  27. Fell DB, Dodds L, MacDonald NE, Allen VM, McNeil S. Influenza vaccination and fetal and neonatal outcomes.Expert Rev Vaccines 2013;12(12):1417-30.
  28. Legge A, Dodds L, Maconald NE, Scott J, McNeil S. Rates and determinants of seasonal influenza vaccination in pregnancy and association with neonatal outcomes. CMAJ 2014;186(4):E157-64.
  29. Fell DB, Sprague AE, Liu N, et al; Better Outcomes Registry and Network (BORN) Ontario. H1N1 influenza vaccination during pregnancy and fetal and neonatal outcomes. Am J Public Health 2012;102(6):e33-40.
  30. Omer SB, Goodman D, Steinhoff MC et al. Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: A retrospective cohort study. PLoS Med 2011;8(5):e1000441.
  31. Richards JL, Hansen C, Bredfeldt C et al. Neonatal outcomes after antenatal influenza immunization during the 2009 H1N1 influenza pandemic: Impact on preterm birth, birth weight, and small for gestational age birth. Clin Infect Dis 2013;56(9):1216-22.
  32. Nordin JD, Kharbanda EO, Vasquez Benitez G et al. Maternal influenza vaccine and risks for preterm or small for gestational age birth. J Pediatr 2014;164(5):1051-7;e2.
  33. Van Santen KL, Bednarczyk RA, Adjaye-Gbewonyo D et al. Effectiveness of pneumococcal conjugate vaccine in infants by maternal influenza vaccination status. Pediatr Infect Dis J 2013;32(11):1180-4.
  34. Luteijn JM, Brown MJ, Dolk H. Influenza and congenital anomalies: A systematic review and meta-analysis. Hum Reprod 2014;29(4):809-23.
  35. Public Health Agency of Canada, National Advisory Committee on Immunization. Statement on seasonal influenza vaccine for 2014-2015: (Accessed October 6, 2014).
  36. Maertens K, De Schutter S, Braeckman T, et al. Breastfeeding after maternal immunisation during pregnancy: Providing immunological protection to the newborn; A review. Vaccine 2014;32(16):1786-92.

Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.

Last updated: Jul 24 2018