By Rebecca B. Perkins, MD, MSc
Professor, Department of Obstetrics and Gynecology, Boston University School of Medicine/Boston Medical Center, Boston
SYNOPSIS: Infants younger than 6 months of age are at risk for severe influenza infections. Vaccination during pregnancy reduces infection and hospitalization risk by nearly 70%.
SOURCE: Fell DB, Russell M, Fung SG, et al. Effectiveness of maternal influenza vaccination during pregnancy against laboratory-confirmed seasonal influenza among infants under 6 months of age in Ontario, Canada. J Infect Dis 2023; Nov 29:jiad539. doi: 10.1093/infdis/jiad539. [Online ahead of print].
Maternal influenza vaccination is recommended for all individuals pregnant during flu season to directly protect pregnant people from severe infections as well as protect newborns via passive antibody transfer.1 However, maternal vaccination rates in the United States are below national targets, with vaccination rates of only 60%, and with lower rates noted for Black women than for white women.2 Prior research shows that pregnant people are at increased risk for influenza complications such as pneumonia and hospitalization, and neonates are at risk for preterm birth and low birthweight, hospitalization, and death.3 Administration of the influenza vaccine in pregnancy reduces influenza infection and complication rates, and vaccination is safe for infants and pregnant people.4,5 However, as vaccine hesitancy has increased in the wake of the COVID-19 pandemic, continuing to provide data on the benefits of influenza vaccination is critical to provide clinicians with the tools and motivation needed to counsel patients.
The article by Fell et al examined the risks of influenza infection and hospitalization among infants aged younger than 6 months by maternal vaccination status.6 Data were collected between 2010 and 2019 in Ontario, Canada, on all influenza tests performed on infants aged younger than 6 months. Infant records were linked to maternal records to determine the effect of maternal vaccination on infant infection. The study reports on all infants aged younger than 6 months in the province of Ontario who underwent influenza testing during flu season.
To minimize erroneous attributions, infants were excluded if they did not have health insurance on the date of specimen collection, were not born in Ontario, if the infant record could not be linked to the maternal record, or if their mother did not have continuous coverage under the Canadian single payer health insurance plan for their entire pregnancy. Maternal flu vaccination status was determined using billing claims. The authors found that vaccine efficacy was 64% (95% confidence interval [CI], 50% to 74%) against infection and 67% against hospitalization (95% CI, 50% to 78%).
COMMENTARY
This study has implications for pregnant individuals and clinicians. Young, otherwise healthy individuals may believe that they are at low risk of influenza complications, but risks rise substantially during pregnancy because of immune changes and reduced lung capacity. In addition, infants aged younger than 6 months have no innate immunity and are too young to receive influenza vaccines. Discussing vaccination with pregnant individuals and trying to encourage vaccine acceptance to avoid vaccine-preventable disease can be challenging for clinicians. Because obstetric providers are the most trusted sources of vaccine information, arming clinicians with knowledge and improving their understanding of vaccine benefits will directly benefit patients. A strong recommendation that vaccination occur that day is most beneficial because patients find it clear and convincing.7
In addition, research has shown that pregnant people’s preferred messages relate to neonatal benefits, and that discussion of maternal influenza risks can be frightening.8 Even patients with low health literacy appreciated understanding that vaccinating the pregnant individual protected the fetus through transfer of placental antibodies.8 Patients may benefit from a simple statement such as, “You’re due for the flu vaccine today. I recommend the flu vaccine for all my pregnant patients. It protects you now, and the antibodies you make pass to the baby so they are protected for the first six months of life.”
REFERENCES
- [No authors listed]. ACOG Committee Opinion No. 741 summary: Maternal immunization. Obstet Gynecol 2018;131:1188-1191.
- Razzaghi H, Kahn KE, Black CL, et al. Influenza and Tdap vaccination coverage among pregnant women – United States, April 2020. MMWR Morb Mortal Wkly Rep 2020;69:1391-1397.
- Rasmussen SA, Jamieson DJ, Uyeki TM. Effects of influenza on pregnant women and infants. Am J Obstet Gynecol 2012;207(3 Suppl):S3-8.
- Zaman K, Roy E, Arifeen SE, et al. Effectiveness of maternal influenza immunization in mothers and infants. N Engl J Med 2008;359:1555-1564.
- Sukumaran L, McCarthy NL, Kharbanda EO, et al. Infant hospitalizations and mortality after maternal vaccination. Pediatrics 2018;141:e20173310.
- Fell DB, Russell M, Fung SG, et al. Effectiveness of maternal influenza vaccination during pregnancy against laboratory-confirmed seasonal influenza among infants under 6 months of age in Ontario, Canada. J Infect Dis 2023; Nov 29. doi:10.1093/infdis/jiad539. [Online ahead of print].
- Fenton AT, Eun TJ, Clark JA, Perkins RB. Indicated or elective? The association of providers’ words with HPV vaccine receipt. Hum Vaccin Immunother 2018;14:2503-2509.
- Fuss TL, Devera JL, Pierre-Joseph N, Perkins RB. Attitudes and communication preferences for vaccines among pregnant women receiving care at a safety-net hospital. Womens Health Issues 2022;32:67-73.
