Influenza vaccine viruses and reagents

Courtesy of NIBSC, HPA UK

Vaccination is the principal measure for preventing influenza and reducing its impact.

Since 1973, WHO has provided formal recommendation for the composition of influenza vaccines based on the information provided by the WHO Global Influenza Surveillance Network (GISN), now the WHO Global Influenza Surveillance and Response System. High yield candidate vaccine viruses are developed by collaboration of laboratories involved in developing reassortants and WHO Collaborating Centres (CCs). Once developed, these candidate reassortants are sent to WHO CCs for characterization of their antigenic and genetic properties before being released to interested institutions on request. Reference reagents are subsequently developed and standardized by Essential Regulatory Laboratories (ERLs), in collaboration with vaccine manufacturers and made available to manufacturers worldwide upon request.

Previous WHO recommendations on the composition of seasonal influenza virus vaccines

Antigenic and genetic characteristics of zoonotic influenza viruses and candidate vaccine viruses developed for potential use in human vaccines


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Why influenza vaccine viruses need to be updated?

  • Influenza vaccination is currently the principal means of reducing or counteracting influenza mortality and morbidity burden in the community.
  • The constantly evolving nature of influenza viruses requires continuous global monitoring and frequent reformulation of influenza vaccines.
  • Rapid spread of influenza viruses during seasonal epidemics and occasional pandemics tightly frames the whole process if vaccine is to be manufactured and delivered on time.
  • A prerequisite of production and supply of an optimal influenza vaccine is the selection and development of optimal candidate vaccine viruses, and the development and availability of vaccine potency reagents.

Selection of vaccine viruses

  • Vaccine virus selection has been conducted by the WHO Global Influenza Surveillance and Response System (GISRS) since 1973.
  • National Influenza Centres (NICs) of GISRS conduct virological surveillance at national level with more than 600,000 clinical specimens tested annually since 2007.
  • Representative specimens and virus isolates are sent to WHO Collaborating Centres (CCs) with more than 5,000 virus isolates characterized by CCs yearly.
  • Collaborative serological studies have been conducted by WHO CCs and Essential Regulatory Laboratories (ERLs) using sera from vaccinees, to determine whether the antibody levels produced by current vaccines are able to react sufficiently against circulating influenza viruses.
  • Twice yearly WHO organizes consultations with experts from WHO CCs, ERLs and other partners to review data generated by GISRS and makes recommendations on influenza vaccine composition for the next northern or southern hemisphere influenza seasons.

Development of candidate vaccine viruses

  • In general influenza wild type A viruses recommended for inclusion in vaccines do not grow efficiently in eggs for large scale production.
  • Two technologies are being used for the development of suitable candidate reassortant vaccine viruses:
    • classical reassortment, available since 1971 to generate hybrid viruses.
    • reverse genetics, a patented technology, available to attenuate highly pathogenic viruses and reassort the attenuated HA and NA with backbone virus.

Vaccine potency reagents

  • Reference antigen and sheep antisera are developed by ERLs in collaboration with vaccine manufacturers, standardized by ERLs, and made available to manufacturers worldwide on request.