Impact of maternal vaccination timing and influenza virus circulation on birth outcomes in rural Nepal

Abstract

Objective: To describe the effect of maternal vaccination on birth outcomes in rural Nepal, modified by timing of vaccination in pregnancy and influenza virus activity.

Methods: A secondary analysis was conducted using data from two annual cohorts of a randomized controlled trial. A total of 3693 pregnant women from Sarlahi District were enrolled between April 25, 2011, and September 9, 2013. All participants were aged 15-40 years and received a trivalent inactivated influenza vaccine or placebo. The outcome measures included birth weight, pregnancy length, low birth weight (<2500 g), preterm birth, and small-for-gestational-age birth.

Results: Data were available on birth weight for 2741 births and on pregnancy length for 3623 births. Maternal vaccination increased mean birthweight by 42 g (95% confidence interval [CI] 8-76). The magnitude of this increase varied by season but was greatest among pregnancies with high influenza virus circulation during the third trimester. Birth weight increased by 111 g (95% CI -51 to 273) when 75%-100% of a pregnancy's third trimester had high influenza virus circulation versus 38 g (95% CI -6 to 81) when 0%-25% of a pregnancy's third trimester had high influenza virus circulation. However, these results were nonsignificant.

Conclusion: Seasonal maternal influenza vaccination in rural Nepal increased birth weight; the magnitude appeared larger during periods of high influenza virus circulation. CLINICALTRIALS.GOV: NCT01034254.

Keywords: Influenza; Low birth weight; Nepal; Pregnancy; Preterm; Small for gestational age; Vaccination.

Figure 1

Mean birth weight in relation to influenza virus circulation.