Influenza vaccine has been shown to decrease the risk of influenza illness among pregnant women and their infants.1 Beginning as early as 1960, influenza vaccination was recommended for pregnant women to prevent influenza virus infection and its complications.2 Since 2004, the US Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices (ACIP), the American College of Obstetricians and Gynecologists (ACOG), and other professional organizations have recommended that all pregnant women receive the inactivated vaccine, regardless of pregnancy trimester, to avoid missed opportunities for vaccination.3
Risks and benefits of vaccination
Pregnant women with influenza are at substantial risk for morbidity and mortality related to influenza. The increased severity of influenza in pregnant women is thought to be related to physiologic changes that occur during pregnancy: heart rate and oxygen consumption increase, lung capacity decreases, and there is a shift away from cell-mediated immunity. One only needs to recall the 2009 influenza A H1N1 pandemic to recount the reports of maternal ICU admission and death in pregnant women.4 Newborn infants born to mothers with influenza during pregnancy, especially mothers with severe illness, are also at increased risk of adverse outcomes due to exposure and lack of immunity.5 Vaccination against influenza may reduce the risk of flu-associated acute respiratory infection in pregnant women by up to one-half.6 Infants born to women who received an influenza vaccine during pregnancy are protected from influenza infection for their first several months of life; this is critical because infants under 6 months of age are dependent on the antibodies conferred in utero and the vaccine is not approved for use in infants younger than 6 months.7,8
Obstetric care provider involvement
Multiple studies have shown that a provider’s recommendation and offer of a vaccine plays a critical role in a patient’s decision to be immunized. In a recent report from the CDC, 68% of pregnant women who received both a recommendation and offer from their physician or other healthcare provider were vaccinated against influenza compared to only 8.5% who received no recommendation.9 Despite some incredible improvements in influenza vaccination coverage in pregnant women during the 2009-10 H1N1 pandemic, influenza vaccination coverage for all pregnant women in the United States remains low, at about 50%.9
Recent report about influenza vaccination and spontaneous abortion
A study published in September in Vaccine reported an association of spontaneous abortion within 28 days of the receipt of influenza vaccination, with a more pronounced association in women who were vaccinated consecutively during the years 2010-2011 and 2011-2012. The median gestational age at the time of miscarriage was 7 weeks, a range in which many miscarriages are either not recognized or do not result in medical attention.10 The miscarriages that came to attention and could be included in the study reflect a limited subset of all the miscarriages that would have occurred in the population. A critical question is whether women who were vaccinated might be especially inclined to have their miscarriage be medically recognized and thus included in the study. To the extent that both receipt of vaccine and obtaining medical care for a miscarriage are correlated, the measure of their association would be biased. The higher risk for women vaccinated in both seasons may indicate an even stronger tendency to obtain medical care and a stronger version of this same problem.
This article received a large amount of press and women may ask questions about receiving the influenza vaccination in pregnancy as we head into flu season. Scientifically it would be very unlikely for the vaccine to be harmful to pregnancy, and there is an abundance of evidence indicating that it is not, in fact, harmful. While this new study should encourage new research to replicate or refute the findings, in balance the totality of the evidence is clearly supportive of the benefits of vaccination outweighing the risks.
Putting the new study in context of other research
Millions of women have received the influenza vaccination in pregnancy and a vast amount of epidemiologic and clinical studies support the safety of inactivated influenza vaccines in pregnant women and their infants.11,12 A number of earlier well-designed studies have not found a link between flu vaccination and any adverse pregnancy outcomes, including miscarriage or stillbirth. A meta-analysis performed to look specifically at the association between influenza immunization and the birth outcomes of stillbirth and spontaneous abortion found that women in the influenza vaccine group had a statistically lower likelihood of stillbirth (relative risk, 0.73; 95% confidence interval [CI], 0.55-0.96) and the pooled estimate for spontaneous abortion based on limited evidence suggested no increase in risk.13
Current stance by ACOG/SMFM/CDC
Given the information noted above, the CDC and the ACIP continue to recommend flu vaccination in pregnancy.12 Both ACOG and the Society for Maternal-Fetal Medicine (SMFM) also support the administration of influenza vaccine in pregnant women stating “SMFM agrees with the study’s authors that there are insufficient data to change the current recommendation and therefore continues to recommend that pregnant women get a flu vaccine any time during pregnancy”14 and “ACOG continues to recommend that all women receive the influenza vaccine. This is particularly important during pregnancy. In evaluating all of the available scientific information, there is insufficient information to support changing the current recommendation which is to offer and encourage routine flu vaccinations during pregnancy regardless of the trimester of pregnancy.”15
We continue to encourage you to advocate for influenza vaccination in your practice based on the compelling evidence that benefits outweigh risks, and that these discussions form the basis for informed decisions by your patients. Further information from ACOG at this http://immunizationforwomen.org/2017-2018-influenza-season may be helpful.
1. Rasmussen SA, Jamieson DJ, Uyeki TM. Effects of influenza on pregnant women and infants. Am J Obstet Gynecol. 2012 Sep;207(3 Suppl):S3-8.
2. Burney LE. Influenza immunization: statement. Public Health Rep. 1960;75:944
3. Fiore AE, Uyeki TM, Broder K, et al. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR Recomm Rep. 2010; 59: 1–62
4. Louie JK, Acosta M, Jamieson DJ, Honein MA, for the California Pandemic (H1N1) Working Group* Severe 2009 H1N1 Influenza in Pregnant and Postpartum Women in California. N Engl J Med. 2010; 362:27-35
5. 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 Sep 4;371(10):918-31.
6. Thompson MG, Li DK, Shifflett P, et al. Effectiveness of seasonal trivalent influenza vaccine for preventing influenza virus illness among pregnant women: a population-based case-control study during the 2010-2011 and 2011-2012 influenza seasons. Pregnancy and Influenza Project Workgroup. Clin Infect Dis. 2014 Feb;58(4):449-57.
7. Tapia MD, Sow SO, Tamboura B, et al. Maternal immunisation with trivalent inactivated influenza vaccine for prevention of influenza in infants in Mali: a prospective, active-controlled, observer-blind, randomised phase 4 trial. Lancet Infect Dis. 2016 Sep;16(9):1026-1035
8. Steinhoff MC, Katz J, Englund JA, et al. Year-round influenza immunisation during pregnancy in Nepal: a phase 4, randomised, placebo-controlled trial. Lancet Infect Dis. 2017 Sep;17(9):981-989.
9. Ding H, Black CL, Ball S, et al; Centers for Disease Control a nd Prevention (CDC). Influenza vaccination coverage among pregnant womenââUnited States, 2014â15 influenza season. MMWR Morb Mortal Wkly Rep. 64(36);1000â1005
10. Donahue JG, Kieke BA, King JP, et al. Association of spontaneous abortion with receipt of inactivated influenza vaccine containing H1N1pdm09 in 2010-11 and 2011-12. Vaccine. 2017 Sep 25;35(40):5314-5322.
11. Kharbanda EO, Vazquez-Benitez G, Shi WX, et al. Assessing the safety of influenza immunization during pregnancy: the Vaccine Safety Datalink. Am J Obstet Gynecol. 2012 Sep;207(3 Suppl):S47-51.
12. Centers for Disease Control and Prevention. Pregnant women & influenza (flu). Available at https://www.cdc.gov/flu/protect/vaccine/pregnant.htm Accessed October 18, 2017.
13. Bratton KN, Wardle MT, Orenstein WA and Saad BO. Maternal Influenza Immunization and Birth Outcomes of Stillbirth and Spontaneous Abortion: A Systematic Review and Meta-analysis Clinical Infectious Diseases® 2015;60(5):e11–9
14. Society for Maternal-Fetal Medicine. Prepare for flu season. Available at https://www.smfm.org/flu Accessed October 18, 2017.
15. American College of Obstetricians and Gynecologists. It is safe to receive flu shot during pregnancy. Available at https://www.acog.org/About-ACOG/News-Room/Statements/2017/It-is-Safe-to-Receive-Flu-Shot-During-Pregnancy Accessed October 18, 2017.