Ten influenza seasons in France: distribution and timing of influenza A and B circulation, 2003-2013.
BACKGROUND
Describing the circulation of influenza viruses and the characteristics of seasonal epidemics remains an essential tool to optimize the strategies of influenza prevention and control. Special attention has been recently paid to influenza B in the context of the availability of a quadrivalent vaccine, containing two influenza B strains.


METHODS
We used data from a practitioners-based influenza surveillance network to describe the circulation of influenza viruses in France from 2003-2004 to 2012-2013. Nasopharyngeal swabs taken from acute respiratory infection (ARI) patients between October and April were tested for influenza. We reported the number of influenza cases by virus type (A, B), subtype (A(H1), A(H3)) and B lineage (Yamagata, Victoria) in each season and determined the frequency of influenza B vaccine mismatch. We estimated weekly incidence of influenza by extrapolating reported influenza cases to the French population. We compared the temporal characteristics of the epidemics caused by influenza A(H1), A(H3) and B.


RESULTS
Overall, 49,919 ARI patients were tested, of which 16,287 (32.6 %) were positive for influenza. Type B virus caused 23.7 % of all influenza cases. Virus subtypes A(H1) and A(H3) caused 51.6 % and 48.4 % of influenza A cases, respectively. Viruses of the B-Yamagata and B-Victoria lineage caused 62.8 % and 37.2 % of influenza B cases, respectively. There was an influenza B vaccine mismatch in three of the five seasons where influenza B caused 10 % or more of all influenza cases. Influenza A(H3) had the highest average value of estimated weekly incidence during the study period. Influenza B peaked an average 3.8 weeks later than influenza A when both virus types were circulating. No differences in the duration of influenza A and B epidemics were observed.


CONCLUSIONS
Influenza A(H3) was the most prevalent influenza type during the study period. Influenza B caused around one fourth of all influenza cases and tended to circulate later than influenza A. The frequency of influenza B vaccine mismatches was substantial. Timely data on the circulation of influenza viruses collected within influenza surveillance systems are essential to optimize influenza prevention and control strategies.
Open Rome (Organize and Promote Epidemiological Network), 67 rue du Poteau, 75018, Paris, France. amos@openrome.org.|Réseau des GROG, 67 rue du Poteau, 75018, Paris, France. amos@openrome.org.
Anne
A
Mosnier
Open Rome (Organize and Promote Epidemiological Network), 67 rue du Poteau, 75018, Paris, France. saverio.caini@gmail.com.
Saverio
S
Caini
Open Rome (Organize and Promote Epidemiological Network), 67 rue du Poteau, 75018, Paris, France. idaviaud@openrome.org.|Réseau des GROG, 67 rue du Poteau, 75018, Paris, France. idaviaud@openrome.org.
Isabelle
I
Daviaud
Réseau des GROG, 67 rue du Poteau, 75018, Paris, France. jl.bensoussan@medsyn.fr.
Jean-Louis
JL
Bensoussan
Laboratoire de Virologie, CHU de Strasbourg, Strasbourg, France. francoise.stoll-keller@chru-strasbourg.fr.
Françoise
F
Stoll-Keller
Open Rome (Organize and Promote Epidemiological Network), 67 rue du Poteau, 75018, Paris, France. bttai@openrome.org.
Tan Tai
TT
Bui
CNR des virus influenzae, CBPE, HCL & Virpath, UCBL, Université de Lyon, Lyon, France. bruno.lina@univ-lyon1.fr.
Bruno
B
Lina
CNR des virus influenzae, GMVR Institut Pasteur, CNRS UMR3569, Université Paris Diderot, Sorbonne Paris Cité, Paris, France. sylvie.van-der-werf@pasteur.fr.
Sylvie
S
Van der Werf
Open Rome (Organize and Promote Epidemiological Network), 67 rue du Poteau, 75018, Paris, France. jmcoco@openrome.org.|Réseau des GROG, 67 rue du Poteau, 75018, Paris, France. jmcoco@openrome.org.
Jean Marie
JM
Cohen
D000328:Adult; D002675:Child, Preschool; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology / Q000302:isolation & purification; D009980:Influenza A virus / Q000276:immunology / Q000302:isolation & purification*; D009981:Influenza B virus / Q000276:immunology / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D008297:Male; D011159:Population Surveillance / Q000379:methods; D012189:Retrospective Studies; D012621:Seasons; D014611:Vaccination
D007252:Influenza Vaccines