Abstract
ABSTRACTHuman influenza is predominantly caused by influenza A virus (IAV) – A/H1N1 and/or A/H3N2 – and influenza B virus (IBV) – B/Victoria and/or B/Yamagata, which co-circulate each season. Influenza surveillance provides important information on seasonal disease burden and circulation, and vaccine content for the following season. To study the circulating influenza subtypes/lineages in western Turkey. Community-based sentinel surveillance results during 2003–2016 (weeks 40–20 each season; but week 21, 2009 through week 20, 2010 during the pandemic) were analyzed. Nasal/nasopharyngeal swabs from patients with influenza-like illness were tested for influenza virus and characterized as A/H1N1, A/H3N2, or IBV. A subset of IBV samples was further characterized as B/Victoria or B/Yamagata. Among 14,429 specimens (9,766 collected during interpandemic influenza seasons; 4,663 during the 2009–2010 pandemic), 3,927 (27.2%) were positive. Excluding the pandemic year (2009–2010), 645 (27.4%) samples were characterized as A/H1N1 or A/H1N1/pdm09, 958 (40.7%) as A/H3N2, and 752 (31.9%) as IBV, but the dominant subtype/lineage varied widely each season. During the pandemic year (2009–2010), 98.3% of cases were A/H1N1/pdm09. IBV accounted for 0–60.2% of positive samples each season. The IBV lineages in circulation matched the vaccine IBV lineage >50% in six seasons and <50% in four seasons; with an overall mismatch of 49.7%. IBV cases tended to peak later than IAV cases within seasons. These results have important implications for vaccine composition and optimal vaccination timing. Quadrivalent vaccines containing both IBV lineages can reduce B-lineage mismatch, thus reducing the burden of IBV disease.
Highlights
Seasonal influenza is a public health problem that affects approximately 5–10% of adults and 20–30% of children worldwide each year, and is responsible for significant influenzarelated morbidity and mortality, especially in high-risk groups, as identified by the World Health Organization (WHO).[1]The causative pathogen, influenza viruses, belongs to the ribonucleic acid virus family Orthomyxoviridae and can be classified into A, B, and C types.[2]
We investigated the results of community-based sentinel surveillance of 13 consecutive influenza seasons (2003-2016) in western Turkey, building upon our previous reports.[14,15]
Since the 2009–2010 pandemic year, our positivity rate reached 29–45% for each season, except for 2012–2013. This is slightly higher than results from sentinel and non-sentinel surveillance in eastern Turkey, where 20–34% of samples were positive during 2010–2015.16
Summary
The causative pathogen, influenza viruses, belongs to the ribonucleic acid virus family Orthomyxoviridae and can be classified into A, B, and C types.[2] Contrary to IAV, IBV almost exclusively infects humans,[3] and is not associated with a pandemic risk. It is acknowledged that IBV is common among younger people, can cause epidemics every few years,[4] and has been associated with a disproportionate number of pediatric influenza deaths.[5]. The most effective way to prevent influenza and its complications is vaccination,[1] among high-risk individuals (i.e. the elderly, children, people with underlying conditions, and healthcare workers).[6,7,8] Current trivalent subunit influenza vaccines (TIVs) are composed of two IAV subtypes
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