The composition of the vaccine for the November 2000 – April 2001 influenza season in the Northern hemisphere has been determined and communicated to vaccine manufacturers by the World Health Organization (WHO), following agreement on its content by international experts. The scientists and researchers gathered in Geneva this week for their annual rendezvous recommended that the influenza vaccine should contain the following three components:

• an A/Moscow/10/99(H3N2)-like virus *
• an A/New Caledonia/20/99(H1N1)-like virus
• a B/Beijing/184/93-like virus +

WHO strongly recommends the use of vaccine as an effective preventive measure against this potentially fatal disease. Anywhere between 50% to 80% of vaccine recipients will be protected against the disease when there is a good match between the vaccine and the strains of influenza virus in circulation. Even in those cases when the vaccine does not fully protect against the disease, severity of illness and the frequency of serious complications are reduced.

Most of the population has been previously infected with or exposed to influenza A(H3N2), influenza A(H1N1) and influenza B viruses and is known to have some degree of residual immunity. As a consequence, one dose of influenza vaccine should be sufficient for all ages except young children. Previously unimmunized children should receive two doses of vaccine within at least four weeks.

Specific vaccine viruses used in each country should be approved by the national control authorities. National public health authorities are responsible for recommendations regarding the use of vaccines.

All WHO recommendations are published in WHO's Weekly Epidemiological Record and communicated to public health authorities, national control authorities and influenza vaccine manufacturers.

The detection of new influenza viruses is made possible thanks to the WHO network for influenza surveillance and control, composed of 110 National Influenza Centres in 82 countries, and through the four WHO Collaborating Centres for Virus Reference and Research on Influenza in Australia, Japan, the United Kingdom of Great Britain and Northern Ireland and the United States of America. This network helps WHO monitor influenza activity in all regions of the world and ensures that virus isolates and information are sent rapidly to the WHO Collaborating Centres for Virus Reference and Research for immediate strain identification.

Recommendations for the composition of vaccines intended for the May 2001 to October 2001 period for the Southern hemisphere will be made by WHO in September 2000. The timing of WHO's recommendations is critical to allow sufficient time for companies to produce the vaccine before the new influenza season starts.

The current influenza season in the Northern hemisphere is characterized by moderate to severe influenza outbreaks in the Americas, Asia and Europe.