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.
J. Katz, None
J. Englund, None
J. Kuypers, None
S. Khatry, None
S. C. Leclerq, None
L. Shrestha, None