Press Release WHO/25
18 February 1998
WHO ANNOUNCES INFLUENZA VACCINE
FORMULA FOR 1998/1999
The composition of the influenza vaccine for the 1998-1999 season has been announced at a meeting of international experts held at the World Health Organization (WHO) headquarters in Geneva. As a result of the meeting, held on 16 and 17 February, the experts changed two of the three influenza vaccine components recommended last year.
Three main antigenic types of influenza viruses are currently circulating among the world's population. These viruses all have a remarkable capacity to change their antigenic characteristics from year to year. They are known as A(H1N1), A(H3N2) and B. At present there is no evidence of current human infection with influenza A(H5N1) virus or evidence of spread beyond the initial focus in Hong Kong, Special Administrative Region of China.
Between October 1997 and February 1998, influenza was reported in Africa, the Americas, Asia, Europe and Oceania. During the first three months of this period, influenza occurred sporadically in many countries in the northern hemisphere while outbreaks continued to be reported in a few countries in the southern hemisphere. In January 1998, North America and some countries in Asia had widespread activity while in Europe influenza increased from early February. Influenza A viruses were predominantly of the A(H3N2) subtype; in some countries influenza A(H1N1) viruses were also frequently isolated. Few laboratory confirmed cases of influenza B have been reported. Following the first case of human influenza A(H5N1) in May 1997, 17 additional cases occurred in November and December in the Hong Kong.
In light of the above, it is recommended that vaccines to be used in the season 1998-1999 contain the following:
an A/Sydney/5/97(H3N2)-like virus;
an A/Beijing/262/95(H1N1)-like virus;
a B/Beijing/184/93-like virus.
WHO is closely monitoring the possible spread of influenza A(H5N1) virus and will publish updated information in the event of further spread. At present it is not justified to make recommendations for the production of an influenza A(H5N1) vaccine for general use.
This year's vaccine composition differs from last year's in that the A/Sydney/5/97(H3N2)-like and A/Beijing/262/95(H1N1)-like virus strains replace the A/Wuhan/359/95(H3N2)-like and A/Bayern/7/95(H1N1)-like virus strains.
As in previous years, the specific viruses used in vaccine manufacturing in each country will need to be approved by the national control authorities.
On Wednesday, 18 February, as happens every year, the group of influenza experts advised national health authorities and pharmaceutical companies on the three selected virus strains that should be used to produce vaccines for the next influenza season. The timing of this recommendation is critical to allow sufficient time for companies to produce the vaccine before the new influenza season starts. The influenza season in the northern hemisphere normally runs from October to March, while in the southern hemisphere it runs from June to August.
Influenza causes epidemics worldwide every year. WHO strongly recommends the use of vaccine as a sound preventive measure against this potentially fatal disease. The degree of protection provided by influenza vaccines varies, depending on the age and immune status of the vaccine recipient, but 50% to 80% of recipients will be protected against disease when there is a good match between the vaccine and strains of influenza that are in circulation. In addition, if the vaccine does not fully protect against disease, the severity of illness and the frequency of serious complications are reduced. National public health authorities are responsible for recommendations regarding the use of the vaccine.
For the adult population, one dose of inactivated vaccine should be adequate. However, previously unimmunized children should receive two doses of vaccine, with an interval of at least four weeks between doses.
The detection of new influenza viruses is made possible through the WHO network for influenza surveillance and control. This network helps WHO to monitor influenza activity in all regions of the world and ensures that the WHO network receives influenza virus isolates and information needed to select the new variants which will be used to produce influenza vaccines for the next influenza season. The programme on influenza surveillance was established in 1948 and the network today involves 110 WHO-recognized National Institutes on Influenza in 82 countries, and four WHO Collaborating Centres for Reference and Research on Influenza at the Centers for Disease Control and Prevention (Atlanta, USA), the National Institute for Medical Research (London, UK), the National Institute of Health (Tokyo, Japan) and the WHO Collaborating Centre on Reference and Research on Influenza (Parkville, Australia).
For further information please contact Gregory Hartl, Health Communications and Public Relations, WHO, Geneva, telephone: (41 22) 791 4458, fax: 41 22 791 4858. E-mail: firstname.lastname@example.org
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