Abstract
BACKGROUND: In tropical Africa, data about influenza-associated illness burden are needed to assess potential benefits of influenza vaccination among pregnant women. We estimated the incidence of influenza among pregnant women and their infants in Siaya County, Kenya. METHODS: We enrolled women at <31 weeks of gestation and conducted weekly follow-up until 6-month postpartum to identify acute respiratory illnesses (ARIs). We defined ARI among mothers as reported cough, rhinorrhoea or sore throat and among infants as maternal-reported cough, difficulty breathing, rhinorrhoea or clinician diagnosis of respiratory illness. We collected nasal/nasopharyngeal and oropharyngeal swabs from mothers/infants with ARI and tested for influenza A and B using molecular assays. We calculated antenatal incidence of laboratory-confirmed influenza among mothers and postnatal incidence among mothers and infants. RESULTS: During June 2015 to May 2020, we analysed data from 3,026 pregnant women at a median gestational age of 16 weeks (interquartile range [IQR], 13, 18) and followed 2,550 infants. Incidence of laboratory-confirmed influenza during pregnancy (10.3 episodes per 1,000 person-months [95% confidence interval {CI} 8.6-11.8]) was twofold higher than in the postpartum period (4.0 [95% CI 2.6-5.5]; p < 0.01). Incidence was significantly higher among human immunodeficiency virus (HIV)-infected pregnant women (15.6 [95% CI 11.0-20.6] vs. 9.1 [95% CI 7.5-10.8]; p < 0.01). Incidence among young infants was 4.4 (95% CI 3.0-5.9) and similar among HIV-exposed and HIV-unexposed infants. CONCLUSION: Our findings suggest a substantial burden of influenza illnesses during pregnancy, with a higher burden among HIV-infected mothers. Kenyan authorities should consider the value of vaccinating pregnant women, especially if HIV infected.