Background: Influenza immunization of pregnant women provides protection of the infant against influenza disease. A potential mechanism of protection is prevention of maternal illness that may result in secondary transmission to infants. We aim to characterize influenza transmission in mother-infant pairs.
Methods: Pregnant mothers were enrolled in a randomized controlled trial of influenza immunization in rural Nepal from April 2011- April 2013. Mothers and infants were surveyed weekly until 180 days post-partum for respiratory illness and mid-nasal swabs were collected at time of illness and tested for influenza virus by reverse-transcriptase polymerase chain reaction (RT-PCR). We defined a transmission episode as a mother-infant pair with an influenza-positive illness within 14 days of each other. Influenza viruses were strain-typed by RT-PCR and/or mass spectrometry.
Results: Seventeen mother-infant transmission episodes occurred with maternal illness preceding infant illness in 12 (70.6%). Of transmission pairs, twelve (70.6%) were influenza B, 3 (17.6%) H3N2 influenza A, 1 (5.9%) H1N1 influenza A, and 1 (5.9%) unspecified influenza A. Five (29.4%) mothers received the influenza vaccine. Successful strain-typing with RT-PCR/mass spectrometry of 11 pairs revealed that 10 (90.9%) were synonymous strains. Figure 1 shows the start of respiratory symptoms and virus type associated with influenza illness in the 17 mother-infant pairs.
Conclusion: Mothers are an important source of infant influenza infection. Transmission was confirmed with nearly all paired transmissions demonstrating a similar strain. The majority of transmission events occurred in non-vaccinated mother-infant pairs.
Figure 1. Influenza transmission events in mother-infant pairs. Symbols represent first day of respiratory symptoms associated with influenza-positive illness.
K. Xue, None
L. Stewart, None
L. Shrestha, None
J. Tielsch, None
M. C. Steinhoff, None
J. Katz, None
S. Khatry, None
S. C. Leclerq, None
J. Bloom, None
J. Englund, GlaxoSmithKline: Investigator , Research grant . MedImmune: Investigator , Research grant . Gilead: Investigator , Research grant . Novavax: Investigator , Research grant . Chimerix: Investigator , Research grant . Alios: Investigator , Research grant .
H. Chu, Sanofi-Pasteur: Grant Investigator , Grant recipient .