Maternal Influenza Vaccination May Protect Infants From Flu

Laurie Barclay, MD

October 07, 2010

October 7, 2010 — Maternal influenza vaccination may be associated with protection from influenza in infants, according to the results of a nonrandomized, prospective, observational cohort study reported online October 4 in the Archives of Pediatric and Adolescent Medicine.

"The US Advisory Committee on Immunization Practices recommends that pregnant women receive influenza vaccine because of the increased risk of influenza complications in pregnant women," write Angelia A. Eick, PhD, from Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, and colleagues. "Maternal influenza vaccination may also confer a benefit to infants born during influenza season, as they are ineligible for vaccination until 6 months of age."

The study goal was to determine the effect of seasonal influenza vaccination during pregnancy on laboratory-confirmed influenza in infants up to 6 months of age. At 6 hospitals on a Navajo reservation and 1 hospital on the White Mountain Apache reservation there were a total of 1169 mother–infant pairs in which delivery occurred during 1 of 3 influenza seasons.

The investigators studied the effect of maternal seasonal influenza vaccination on laboratory-confirmed influenza in the infants, as well as influenza-like illness (ILI), hospitalization for ILI, and influenza hemagglutinin inhibition antibody titers in the infants. The analysis included 160 mother–infant pairs in whom serum was collected.

ILI hospitalization occurred in 193 infants (17%), and ILI outpatient visit only in 412 infants (36%), whereas 555 infants (48%) had no ILI episodes. For infants born to unvaccinated mothers, the ILI incidence rate was 7.2 per 1000 person-days compared with 6.7 per 1000 person-days for infants born to vaccinated mothers.

Risk for laboratory-confirmed influenza virus infection was 41% lower in infants born to influenza-vaccinated women than in those born to unvaccinated women (relative risk [RR],0.59; 95% confidence interval [CI], 0.37 - 0.93), and risk for ILI hospitalization was 39% lower (RR, 0.61; 95% CI, 0.45 - 0.84).

For all 8 influenza virus strains tested, hemagglutinin inhibition antibody titers at birth and at 2 to 3 months of age were significantly higher in infants born to mothers vaccinated against influenza than in infants of unvaccinated women.

"Maternal influenza vaccination was significantly associated with reduced risk of influenza virus infection and hospitalization for an ILI up to 6 months of age and increased influenza antibody titers in infants through 2 to 3 months of age," the study authors write.

Limitations of this study include possible uncontrolled residual confounding, the performance of the study during 3 relatively mild influenza seasons, and the incomplete sensitivity of serologic detection for influenza virus infection.

"Although influenza vaccination is recommended for pregnant women to reduce their risk of influenza complications, these findings provide support for the added benefit of protecting infants from influenza virus infection up to 6 months, the period when infants are not eligible for influenza vaccination but are at highest risk of severe influenza illness," the study authors conclude. "These findings are particularly relevant with the emergence of 2009 pandemic influenza A (H1N1) virus, which had a substantial effect on pregnant women and high hospitalization rates among young infants."

In an accompanying editorial, Justin R. Ortiz, MD, and Kathleen M. Neuzil, MD, MPH, from the Vaccine Development Global Program, PATH, in Seattle, Washington, agree that this study supports a recommendation that all pregnant women receive influenza vaccine to decrease complications of influenza during their pregnancies.

"The additional benefits of maternal influenza vaccination to the newborn, as demonstrated in the Bangladesh and White Mountain Apache and Navajo communities, should catalyze efforts to improve vaccination rates in countries with existing maternal immunization recommendations," Dr. Ortiz and Dr. Neuzil write. "Likewise, these data should encourage the adoption of vaccination guidelines in countries without such recommendations. Maternal influenza vaccination targets 2 high-risk groups with 1 vaccine dose — we can't afford not to act."

The National Vaccine Program Office, Department of Health and Human Services, the Office of Minority Women's Health, Centers for Disease Control and Prevention, Aventis-Pasteur, and Evans-Powderject supported this study. One of the study authors (Dr. O'Brien) reports receiving grants for research projects unrelated to this article from Med-Immune and Pfizer and serving on expert advisory committees for pneumococcal vaccines from Sanofi-Pasteur; all 3 companies manufacture influenza vaccine. Dr. Ortiz and Dr. Neuzil have disclosed no relevant financial relationships.

Arch Pediatr Adolesc Med. Published online October 4, 2010.

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