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.

[The French Committee for the prevention and control of influenza and the 2009 influenza pandemic: Lessons learnt]. / Comité de lutte contre la grippe et la pandémie 2009 : retour d'expérience.

The Committee for the Prevention and Control of Influenza (Comité de lutte contre la Grippe - CLCG) is an advisory committee to the French Health Minister for a medical and scientific collective expertise on the measures to be implemented to control or to reduce the impact of an epidemic or a pandemic of influenza. Appointed by decree, the CLCG consists of ex-officio members; representatives of French Agencies strongly involved by influenza and qualified personalities, representing various fields of expertise. Collective expertise is based on consensus after thorough collective discussion. A notice is drafted in reply to every official question and passed on either to the Chief Medical Officer, or, when the question concerns vaccines, to the Technical Committee of the vaccinations for which the CLCG acted as a working group. The CLCG was extremely active throughout the pandemic. The objective of this article is to describe in a factual way its output throughout this period of sanitary crisis. This article presents and compare chronologically and in a factual way the state of the scientific knowledge about influenza due to the A(H1N1)pdm09 virus and the CLCG notices. Between the alert launched by the WHO the 24th of April and the 31st of December 2009, CLCG met on 40 occasions. Its work dealt in particular with patient care, recommendations on medical treatment (antivirals, seasonal and pandemic vaccines), and on virological diagnosis. Whatever the defects of its expertise delivered in a context of urgency, which was a difficult exercise, the CLCG fulfilled its advisory to the health authorities. However, the pandemic experience showed that this expertise must be improved by insuring the recognition and the visibility of the advisory committee and by defining their exact position in the chain of decision.