Influenza B burden during seasonal influenza epidemics in France.

Abstract Context Seasonal flu outbreaks are linked to the circulation of influenza virus type A or B. Special attention has always been paid to influenza A epidemics; but recently, several studies have investigated the impact of influenza B virus epidemics, particularly as, since the 1980s, two antigenically different influenza B lineages co-circulate, raising the issue of vaccine matching. Objectives We present the results of influenza B burden during nine influenza seasons (2003–2013) and vaccine matching of the circulating lineages. Patients and methods Clinical and virological influenza surveillance data, collected by the Regional Groups for Influenza Surveillance Network in France, allows for studying the burden of influenza in the practice of the population of ambulatory care physicians. Results and conclusion Our analysis is based on 37,801 samples, of which 12,036 were virologically confirmed influenza cases (31.8%), including 3576 cases of influenza B (29.7% of influenza cases). Influenza B viruses significantly circulated during six seasons. For each season, the influenza B epidemic peaked later than the influenza A epidemic. Influenza B is very common in children of school age but also affects other age groups. Finally, more than one-third of the analyzed influenza B viruses belonged to a different lineage than the one used in the composition of the trivalent vaccine. Our results are comparable to those described in other countries.