The Evolving History of Influenza Viruses and Influenza Vaccines

Authors and Disclosures

Claude Hannoun

Institut Pasteur, Paris, France +33 146 568 264 chann@club-internet.fr

Key Issues

• Influenza virus was first isolated 80 years ago in 1933.

• The first influenza vaccine was a monovalent live-attenuated vaccine, which was used in Russia until recently.

• In 1940, a second strain of influenza virus was isolated; this was named influenza B and the first strain was named influenza A.

• During the Second World War, the first inactivated vaccine was produced by the U.S. army and started to be used widely in 1944, particularly for the American troops in Europe and was then extended to civilians in 1945.

• In 1947, the vaccine was unexpectedly less efficient; it was discovered that the antigenic composition of the circulating virus had changed and antigenic drift was discovered.

• Two surface proteins, HA and NA, determine the antigenic properties of influenza virus strains.

• In 1958, a new strain of influenza A with different HA and NA was identified and antigenic shift was discovered; the need for a trivalent vaccine was recognized.

• Technical advances have made it possible to produce reassortant strains between wild-type viruses (for their antigenic properties) and culture-adapted strains (for their replication properties).

• Since 1973, the WHO issues recommendations for the composition of influenza vaccines, based on worldwide surveillance systems and the prediction of the most likely strains to be circulating; since 1999, they issued separate recommendations for the northern and southern hemispheres.

• In 2013, the WHO recommendations included a second influenza B strain allowing countries to decide to recommend a trivalent or a quadrivalent influenza vaccine.