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Maternal influenza immunization may improve fetal outcomes
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VANCOUVER — Pregnant women receiving influenza immunization may be less likely to deliver infants who are small for gestational age, according to results presented at the 48th Annual Meeting of the Infectious Diseases Society of America.
Mark C. Steinhoff, MD, of the Global Health Center at Cincinnati Children’s Hospital in Cincinnati, Ohio, presented the results. “The consequences of influenza infection in pregnant women and young infants may be serious, but may be mitigated by immunization of the pregnant mother,” he said.
Steinhoff noted that there are limited data on the fetal effects of antenatal influenza vaccination.
The researchers analyzed data from a blinded, randomized influenza vaccine trial in 340 pregnant women from Bangladesh to assess the effect of maternal immunization on in utero development and fetal and newborn outcomes.
The trial was conducted from August 2004 to December 2005, and the results were initially published in the New England Journal of Medicine in 2008.
Women in the third trimester were randomized to receive either the control pneumococcal vaccine or inactivated influenza vaccine.
Primary endpoints included mean birth weights, the proportions of infants who were small for gestational age (defined as <10% weight for gestational age), premature (delivered <37 weeks) or with low birth weight (defined as <2.5kg).
The proportion of infants who were small for gestational age was 38% in the control group and 26% in the influenza vaccine group (D–32%; RR=0.68; P=.03), according to the results. “There was a non-significant increase in mean birth weights,” Steinhoff said.
No differences in rates of prematurity or low birth weight were observed between the two arms.
“Analysis of these effects by season show that the mean birth weight (D+7%) and proportion SGA (D–47%) were significantly different (P=.02 for both) between vaccine groups during the interval of greater influenza vaccine clinical effectiveness,” the researchers wrote.
Steinhoff clarified the seasonal impact of the vaccine. “As the season develops, there is much more influenza in unvaccinated mothers than in vaccinated mothers,” he said. “Before Jan. 31, there was a small difference in birth weights. After Feb. 1, there was a 200 gram difference in birth weights, which is quite substantial, and a 57% reduction in children born [small for gestational age].”
Steinhoff concluded that antenatal maternal influenza immunization may be linked to improved fetal outcomes in this cohort of pregnant Bangladeshi women.
“On one hand, with regard to the particulars, this is a new finding,” he said. “On the other hand, this is not new at all: if you prevent disease in the mother, you might have better outcomes in the infant.” – by Rob Volansky
For more information:
- Steinhoff MC. #176 Influenza Immunization in Pregnancy Influences In Utero Development and Fetal Outcomes: Observations from a Randomized Controlled Trial. Presented at: the IDSA 48th Annual Meeting. Oct. 21-24, 2010; Vancouver, B.C.
- Steinhoff MC. NEJM. 2008; 359:1555-1564.
Disclosure:
Steinhoff reported being a consultant with Novartis and being a grant investigator with the Bill and Melinda Gates Foundation, GlaxoSmithKline, Merck, Sanofi-Aventis, the Thrasher Research Fund, the US Agency for International Development and Wyeth Pharmaceuticals.
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