1898. Evaluation of year-round maternal influenza immunization in tropical SE Asia: a placebo-controlled randomized trial
Session: Poster Abstract Session: Vaccines: Influenza
Saturday, October 10, 2015
Room: Poster Hall
Background: Influenza in pregnancy is associated with adverse outcomes in mother and fetus, but maternal influenza immunization reduces maternal infection, improves fetal outcomes, and provides passive protection to young infants.  Antenatal influenza immunization has been recommended by many countries and WHO.  Because influenza virus circulation in tropical settings occurs throughout the year, we conducted a placebo-controlled randomized trial of influenza immunization year-round in two annual cohorts to assess the effect of this strategy on maternal and infant outcomes.

Methods:  We enrolled and immunized two cohorts of pregnant women in the tropical terai region of southern Nepal from April 2011 thru Sept 2013.  Women between 17 and 36 weeks of pregnancy were randomized to receive influenza vaccine or a saline.  WHO-recommended northern and southern hemisphere influenza vaccine (Vaxigrip, SanofiPasteur) was provided (N= Oct-Apr, S=May-Sept).  Birthweight and gestational age of newborns were recorded, and pre-and post- immunization serum samples and cord blood were collected in a subset of women. Weekly home visits during pregnancy and infancy occurred, with mid-nasal swabs for PCR and viral cultures obtained during maternal acute febrile infections, or in infants with any respiratory symptom. 

Results: 3,693 mothers were recruited, with 3,645 live births. The rate of adverse outcomes of pregnancy and delivery were similar in both groups.  Flu virus was present in 28/36 months surveillance, with 3 or more influenza strains circulating during 9 months.  Influenza was  detected in 445 specimens. Substantial variation of vaccine effect appeared related to variation in antigenic match between vaccine and circulating viruses. Overall, influenza vaccine reduced laboratory-confirmed flu infection in mothers by 31% (-11, 56 [95% CI]) and by 30% (5, 49) in 0-6 month infants.  In immunized women, the rate of low-birth weight infants was reduced by 15% (3,25), SGA was decreased by 8% (-2, 17), and mean birth weight of infants was increased by 43g (9, 77g).

Conclusion: In this SE Asian tropical region, the strategy of year-round immunization with recommended influenza vaccines appears to have a positive impact in mothers and infants despite influenza antigenic variation.

Mark Steinhoff, MD, Infectious Disease, Cincinnati Childrens Hospital and Medical center, Cincinnati, OH, James Tielsch, PhD, Global Health, George Washington University, Washington, DC, Joanne Katz, ScD, Johns Hopkins University, Baltimore, MD, Janet Englund, MD, FIDSA, Seattle Children's Hospital, Seattle, WA, Jane Kuypers, PhD, University of Washington, Seattle, WA, Subarna Khatry, MBBS, DOMS, NNIPS, Kathmandu, Nepal, Steven C Leclerq, MPH, NNIPS, Baltimore, MD, Laxman Shrestha, MBBS, MD, Pediatrics and Child Health, Institute of Medicine, Tribhuvan University, Kathmandu, Nepal and Mother'sGift Project Nepal

Disclosures:

M. Steinhoff, None

J. Tielsch, None

J. Katz, None

J. Englund, None

J. Kuypers, None

S. Khatry, None

S. C. Leclerq, None

L. Shrestha, None

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