The composition of the vaccine for year 2001-2002
(Northern Hemisphere influenza season) has been decided and communicated
to vaccine manufacturers by the World Health Organization (WHO),
following agreement on its content by international experts at a WHO
meeting held in Geneva, Switzerland this week. The experts recommended
that the influenza vaccine for 2001-2002 (Northern Hemisphere) contain
the following three components:
- an A/New Caledonia/20/99(H1N1)-like virus
- an A/Moscow/10/99(H3N2)-like virus
- a B/Sichuan/379/99-like virus
Between October 2000 and February 2001, mild to
moderate influenza activity was reported throughout the world. Influenza
A(H1N1), A(H3N2) and B viruses continued to be isolated in the southern
hemisphere, mainly from sporadic cases. In the northern hemisphere,
influenza activity was initially reported during the third week of
November, increased in December and continued through February.
Influenza activity was mainly due to influenza
A(H1N1) virus, which co-circulated with influenza B viruses in some
countries. Influenza A(H3N2) viruses were isolated sporadically. In most
countries, the greatest impact was in children and young adults.
WHO strongly recommends the use of vaccine as an
effective preventive measure against this potentially fatal disease.
About 50% to 80% of vaccine recipients will be protected against the
disease when there is good match between the vaccine and strains of
influenza virus that are in circulation. In cases where 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 with an interval of at least four weeks.
The 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
All WHO recommendations are published in WHO’s
Weekly Epidemiological Record (WER) and communicated to public health
authorities, national control authorities and influenza vaccine
The detection of new influenza viruses is made
possible through the WHO network for influenza surveillance and control
composed of 110 National Influenza Centres in 82 countries and the four
WHO Collaborating Centres for Reference and Research on Influenza in
Atlanta (USA), London (UK), Melbourne (Australia) and Tokyo (Japan).
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 May 2002 to October 2002 (southern hemisphere) will be made
by WHO in September 2001. The timing of WHO's recommendations is
critical to allow sufficient time for companies to produce the vaccine
before the new influenza season starts.