WHO Global Influenza Surveillance Network

Objectives

The WHO Global Influenza Surveillance Network enables WHO to recommend twice annually the content of the influenza vaccine for the subsequent influenza season (current recommendations.) More than 250 million doses of influenza vaccine are produced annually which contain the WHO recommended influenza strains.

Frequent updating of the influenza vaccine content is necessary as influenza viruses are permanently evolving. Only a vaccine whose virus strains match the circulating influenza viruses will protect recipients efficiently from influenza disease and death.

The WHO Influenza Surveillance Network serves also as a global alert mechanism for the emergence of influenza viruses with pandemic potential. Its activities have contributed greatly to the understanding of influenza epidemiology. The network was established in 1952, after a WHO Expert Committee recommended that through an international network of laboratories, WHO would be able to advise WHO Member States as to “what influenza control measures are useful, useless or harmful”.

Components

The main components of the WHO Global Influenza Surveillance Network are National Influenza Centres (NICs) which sample patients with influenza-like-illness and submit representative isolates to WHO Collaborating Centres (WHO CCs) for antigenic and genetic analyses. NICs, WHO CCs and WHO form the WHO Global Influenza Surveillance Network, with collaboration based on agreed terms of reference.

Currently, 122 institutions from 94 countries are recognized by WHO as National Influenza Centres. A recent comprehensive analysis on the capacities and activities of these NICs has revealed that c. 87 of them participate actively in the WHO Network. In addition, various other laboratories have regularly submitted influenza viruses to the Programme in the past years.

Operations

Annually, the NICs collect more than 175 000 patient samples and submit around 2 000 viruses to the WHO CCs for antigenic and genetic analyses. WHO CCs provide all NICs with a kit of diagnostic reagents containing polyclonal sera, monoclonal antibodies and viral antigens for relevant influenza strains. These kits are updated and distributed annually to ensure standardized analysis of current strains and submission of antigenic variants to WHO CCs for detailed analysis.

There are four WHO Collaborating Centres that participate in the WHO Global Influenza Surveillance Network (in Australia, Japan, United Kingdom, and United States). The WHO CCs perform, at no cost to the WHO Network, antigenic and genetic analyses of isolates received from NICs and maintain repositories of different virus strains.

Most viruses sent to WHO CCs are sequenced (RT-PCR) to find out if these viruses are evolving away from currently circulating strains and from vaccine strains. Sequencing of genes encoding for the antigenic portion of Haemagglutinin protein (HA1 domain) and the Neuraminidase is a sensitive method to examine the degree of change in these genes in virus isolates and the direction that these changes may be taking.

In addition to genetic and antigenic analyses of influenza viruses, the WHO CCs jointly with key national laboratories involved in registration and quality control of influenza vaccines (Australia, United Kingdom, United States) collaborate annually on serological studies to obtain evidence as to whether the current vaccines induce satisfactory antibody levels to new epidemic strains.

Future

The WHO Global Influenza Surveillance Network needs to increase its geographical coverage and to become a highly interactive network of NICs and WHO CCs. Increased availability of electronic communication will support real time reporting of both virological isolations and epidemiological data and facilitate rapid detection of emerging variant or pandemic strains. This will facilitate linking disease surveillance and virological information, improve regional and global communicable disease response and enable exchange and collaboration between NICs.