[Natural history of influenza]. / Histoire naturelle de la grippe.

Influenza is known as a human disease, but many influenza viruses can be found in several other animal species. In some it induces a disease similar to man's infection with a major respiratory tropism. In others the disease is quite different, like the systemic infection of fowl plague. In others, it can be totally asymptomatic. The main species concerned are birds, horse, pig, felines, canines, marine mammals and mustelids. The mechanisms of interspecies transmission of the virus are now better understood and they condition influenza epidemiology. Lessons from the study of past pandemics and other manifestations of influenza during 20th century help to design the tools and procedures for managing an eventual new pandemic.

[Quadrivalent influenza vaccine: What is changed and what are the benefits?] / Vaccin grippal quadrivalent : quels changements pour quels bénéfices ?

Currently, circulating viruses responsible for annual seasonal influenza epidemics belong to two influenza A subtypes, A(H1N1) and A(H3N2), and to two antigenically distinct type B lineages, B/Yamagata and B/Victoria lineages. Like diseases due to influenza A virus, influenza B virus diseases may have severe consequences and should be prevented. Until now, in France, the vaccines used to prevent seasonal influenza were trivalent, systematically targeting viruses belonging to both A subtypes and to one or other of the B lineages. The protective efficacy of trivalent vaccines is diminished during the seasons when viruses belonging to both B lineages cocirculated or when the circulating dominant type B virus belonged to a lineage different from that targeted by the vaccine strain. By targeting viruses belonging to both B lineages, quadrivalent vaccines improve the antigenic concordance between circulating and vaccine type B strains. Three inactivated quadrivalent vaccines are authorized for marketing in France and should be available for the 2018-2019 season. It is expected that, by providing enlarged protection, these quadrivalent influenza vaccines will improve vaccine efficacy, the confidence in immunization of the public, the satisfaction of health professionals, and ultimately will help to complete immunization coverage.

The evolving history of influenza viruses and influenza vaccines.

The isolation of influenza virus 80 years ago in 1933 very quickly led to the development of the first generation of live-attenuated vaccines. The first inactivated influenza vaccine was monovalent (influenza A). In 1942, a bivalent vaccine was produced after the discovery of influenza B. It was later discovered that influenza viruses mutated leading to antigenic changes. Since 1973, the WHO has issued annual recommendations for the composition of the influenza vaccine based on results from surveillance systems that identify currently circulating strains. In 1978, the first trivalent vaccine included two influenza A strains and one influenza B strain. Currently, there are two influenza B lineages circulating; in the latest WHO recommendations, it is suggested that a second B strain could be added to give a quadrivalent vaccine. The history of influenza vaccine and the associated technology shows how the vaccine has evolved to match the evolution of influenza viruses.