中央アフリカ共和国における2015年から2018年までのインフルエンザサーベイランス：ワクチン接種および治療戦略への情報提供

Surveillance of influenza infections and virus characterisation are essential to guide prevention strategies. In the Central African Republic (CAR), data on influenza viruses are patchy and poorly documented.

To study the clinical, seasonal, genetic and phenotypic characteristics of influenza viruses circulating in the CAR population.

From January 2015 to December 2018, the presence of influenza A and B viruses in patients presenting with influenza-like illness (ILI) symptoms or severe acute respiratory infections (SARI) was investigated by RT-qPCR. Influenza genetic diversity was evaluated by phylogenetic analyses, and antigenic properties were investigated by haemagglutination inhibition assays, whereas reduced susceptibility to neuraminidase inhibitors was assessed through the presence of known genetic markers and neuraminidase assay. The relationship between patients' clinical characteristics and infection status was investigated using statistical analyses.

Over the surveillance period influenza viruses were detected in 9.7% of samples (n = 6134), with the highest intensity of circulation occurring in 2016 (15.8%), attributed mainly to A(H3N2). Periods of increased influenza transmission (June to October) generally coincided with rainy seasons; however, variations in terms of monthly distribution of cases between years were evident. Hospitalisation rates (SARI) were most frequent in infants (0-11 months, 37.9%) and young children (1-4 years, 24.8%), whereas influenza prevalences were highest in the 15-49 (12.0%) and ≥ 50 (15.2%) years old categories. A new A(H1N1)pdm09 6B.1 hemagglutinin subgroup characterised by amino acid substitutions S84N, S162N and I216T was detected in 2015, with associated antigenic drift, and subsequently, two of these viruses showed highly reduced inhibition by oseltamivir.

This study showcases the value of local influenza sentinel networks to specifically inform vaccination strategies and highlights the need for improved strain characterisation in tropical regions.