European Influenza Surveillance Scheme: annual report 2004-2005 influenza season.

During the 2004-2005 season, 26 countries actively reported data to EISS and the scheme
included 30 national reference laboratories, at least 12,000 sentinel physicians and
covered a total population of 445 million inhabitants. The influenza season started in late
December 2004 and first occurred in the southwest (Spain, United Kingdom and Ireland).
Influenza activity then moved gradually east across Europe during January and early
February 2005 and there was more of a south north movement during late February till
late March. The intensity of clinical activity was in ten out of 23 countries (no data for
three countries) higher than during the 2003-2004 season and lower or equal in the other
13 countries. The highest consultation incidences were generally observed among
children aged 0-14.

Participants
The European Influenza Surveillance Scheme (EISS) has grown considerably over the
last nine years and included 21 EU countries, Norway, Romania and Switzerland during
the 2004-2005 season. Six new members joined the scheme: Austria and Finland at the
start of the season and Cyprus, Estonia, Hungary and Greece at the end of it. By the end
of the 2004-2005 season, all 25 EU countries were a member of EISS.
The EISS Co-ordination Centre is based at NIVEL in Utrecht, the Netherlands since 1999 and works in close collaboration with ECDC (www.ecdc.eu.int).

Virology
The predominant virus strain was influenza A (83% of total detections) of the H3 subtype
(85% of H-subtyped A viruses), with fewer influenza B (17% of total detections) or
A(H1) viruses (15% of H-subtyped A viruses) detected. The vast majority of A(H3)
viruses were similar to the reference strains A/Wellington/1/2004 (H3N2) and,
subsequently, A/California/7/2004 (H3N2) that are closely related drift variants of the
A/Fujian/411/2002 (H3N2) prototype vaccine strain. The B viruses co-circulated with A
viruses during the whole influenza season in 11 out of 24 countries (no data for two
countries). Seven of these were located in the northeast of Europe and in these countries
the proportion of B viruses was higher (range: 31-60%) than in the rest of Europe (range:
6-26%). In 13 out of 24 countries the B viruses circulated relatively late in the season.
About 43% of all antigenically characterised B viruses were B/Hong Kong/330/2001-like
(B/Victoria/2/87 lineage), a strain that is distinguishable from the vaccine influenza B
strain, which was a B/Yamagata/16/88 lineage virus.
The composition of the 2005-2006 influenza vaccine has been modified compared to the
2004-2005 season and includes a new A(H3N2) component: an A/California/7/2004
(H3N2)-like virus.

Background
Influenza is an important public health problem in Europe. Influenza surveillance networks in Europe have co-operated and shared information since the mid-1980s. They have done this as influenza is a communicable disease that spreads rapidly and efficiently; this means that it is beneficial for countries to be informed about influenza activity (clinical incidence and types/subtypes/strains) in neighbouring
countries. Other benefits are that surveillance systems can learn from each other and initiate common surveillance and/or research projects. The threat of an influenza pandemic has further encouraged this collaboration. During a pandemic, EISS would provide rapid, open and detailed information on the epidemiological and virological spread of influenza in Europe.