Influenza activity is at out-of-season levels in Europe
The EuroFlu bulletin describes and comments on influenza activity in the 53 Member States in the WHO European Region to provide information to public health specialists, clinicians and the public on the timing of the influenza season, the spread of influenza, the prevalence and characteristics of circulating viruses (type, subtype and lineage) and severity.
For a description of influenza surveillance in the WHO European Region see below.
During week 18/2013, 342 specimens tested positive for influenza, with 224 (66%) positive for influenza B, similar to the previous three weeks (Fig. 1). For total weekly influenza detections (sentinel and non-sentinel), the proportion of influenza A viruses in relation to influenza B has gradually decreased since week 03/2013, when type A viruses represented 76% of the total.
Of the 48 influenza A viruses that were subtyped during week 18/2013, 16 (33%) were influenza A(H1N1)pdm09 and 32 (67%) influenza A(H3N2) (Fig. 2a).
Since the beginning of the season (week 40/2012), 95 070 influenza viruses from sentinel and non-sentinel sources have been detected and typed. Cumulatively, 59 534 viruses (63%) were influenza A and 35 536 (37%) influenza B (Fig. 2b). Cumulatively, influenza A has been the most commonly detected virus since week 47/2012. Of the 38 292 influenza A viruses that have been subtyped, 25 492 (67%) were A(H1N1)pdm09 and 12 800 (33%) were A(H3N2).
In addition, the lineage for 5822 influenza B viruses has been determined: 5341 (92%) belonged to the B/Yamagata lineage and 481 (8%) to B/Victoria.
Owing to the low number of viruses detected during week 18/2013 in most countries, only a few reported on dominant virus type: influenza B in Georgia, Germany, Latvia, Lithuania and the Russian Federation, and influenza A in Finland, Greece and the United Kingdom (England and Wales); the United Kingdom (Scotland) reported co-dominance of influenza A and B (Map 1).
For the 2012/2013 northern hemisphere influenza season, WHO recommends inclusion of A/California/7/2009 (H1N1)pdm09-like, A/Victoria/361/2011 (H3N2)-like and B/Wisconsin/1/2010-like (from the B/Yamagata lineage) viruses in vaccines (see more at the WHO headquarters web site).
For the recommendations for the 2013/2014 northern hemisphere influenza season (see the WHO headquarters web site).
Since week 40/2012, 5467 influenza viruses characterized antigenically by 17 countries (Austria, Bulgaria, the Czech Republic, Denmark, Germany, Greece, Italy, Latvia, Portugal, the Republic of Moldova, Romania, the Russian Federation, Slovakia, Slovenia, Spain, Switzerland and the United Kingdom (England and Scotland)). The great majority corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3). The United Kingdom characterized 1420 of these viruses (26%). Scotland reported on 499 (32%) of the 1583 A/Victoria/361/2011 (H3N2)-like viruses characterized this season. 16 countries (Austria, Belgium, Denmark, Finland, Germany, Greece, Ireland, Italy, the Netherlands, Norway, Portugal, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom (Scotland)) have characterized 1642 influenza viruses genetically (Fig. 4).
# Included in the WHO-recommended composition of influenza virus vaccines for use in the 2012/2013 northern hemisphere influenza season.
* Included in the WHO-recommended composition of influenza virus vaccines for use in the 2013 southern hemisphere influenza season.
Both A(H1N1)pdm09 and A(H3N2) viruses have evolved to fall into a number of different genetic groups, which are all antigenically similar to their prototype viruses, egg-propagated A/California/7/2009 and cell-propagated A/Victoria/361/2011, respectively. However, the A/Victoria/361/2011 egg-propagated vaccine virus has egg-induced antigenic changes compared with the cell-propagated A/Victoria/361/2011virus. Influenza B viruses of the B/Victoria/2/87 and the B/Yamagata/16/88 lineages are co-circulating in the Region with dominance of the B/Yamagata lineage viruses (~90%). Influenza B viruses of the B/Victoria lineage all fall within the B/Brisbane/60/2008 genetic clade and are antigenically indistinguishable. B/Yamagata lineage viruses fall into two distinct genetic clades, represented by B/Estonia/55669/2011 (Clade 2) and B/Wisconsin/1/2010 (Clade 3), respectively, with the proportion of viruses in Clade 2 markedly increasing. Viruses in these clades can be distinguished antigenically from each other by some post-infection ferret antisera, but remain antigenically similar to the current vaccine virus, B/Wisconsin/1/2010.
Cumulatively since week 40/2012, 12 countries (Denmark, Germany, Greece, the Netherlands, Norway, Portugal, Romania, the Russian Federation, Spain, Sweden, Switzerland and the United Kingdom) have screened 1400 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.
Of the 697 A(H1N1)pdm09 viruses tested, 684 showed susceptibility to both drugs while 13 viruses (2%) carried the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir. Of these 13 viruses, 1 from the Russian Federation was detected in a hospitalized patient not exposed to oseltamivir through treatment; 1 from Germany was detected in a hospitalized patient with unknown exposure to the neuraminidase inhibitors; 2 viruses from the United Kingdom were detected in outpatients not exposed to oseltamivir through treatment; 6 viruses were detected in hospitalized patients exposed to oseltamivir through treatment (1 from Denmark, 4 from Germany and 1 from Sweden) and 3 viruses were detected in hospitalized immunocompromised patients exposed to oseltamivir through treatment (2 from the Netherlands and 1 from Switzerland).
The 296 influenza A(H3N2) viruses tested showed susceptibility to both drugs. Of the 407 influenza B viruses tested, 406 showed susceptibility to both drugs; 1 virus showing reduced inhibition by oseltamivir, and normal inhibition by zanamivir, was detected in the United Kingdom in an outpatient without exposure to antiviral treatment.
There is no indication of the spread of resistant viruses.
The 105 influenza A(H1N1)pdm09 and 50 influenza A(H3N2) viruses screened for susceptibility to adamantanes were found to be resistant.
During week 18/2013, all countries but 1 reported low influenza activity (Map 2). Most countries in the Region reported decreasing trends (Map 4) and no or sporadic influenza activity in week 18/2013 (Map 3).
ILI and ARI consultation rates were below the national baselines or at pre-season levels in all countries reporting clinical data during week 18/2013.
Click on the maps for more detailed information.
For week 18/2013, the percentage of sentinel specimens testing positive for influenza remained low: 197 sentinel specimens were tested, of which 21 (11%) were positive for influenza (Fig. 5). This decreasing trend has continued since the peak for the season, around week 07/2013.
In the 4 countries testing 20 or more sentinel specimens, influenza positivity ranged from 0% to 9%, with a median of 7% (mean: 6%).
| Of the 21 influenza-positive specimens from sentinel sources, 81% were positive for influenza B. Influenza B has been prevalent for several weeks in countries where circulation of A(H1N1)pdm09 has decreased. Fig. 6b gives a detailed overview of cumulative influenza virus detections by type and subtype since week 40/2012.
for a detailed overview in a table format. || |
In week 18/2013 the number of SARI hospitalizations, along with the influenza positivity rate among cases, returned to pre-season levels in most of the countries taking part in hospital surveillance for SARI (Fig. 7).
| For week 18/2013, only 4 countries (Armenia, Belarus, Georgia and Kyrgyzstan) reported a total of 5 influenza detections all of which were influenza B, in line with the detections reported from outpatient surveillance (Fig. 8a). Since week 40/2012, 7188 SARI specimens have been collected and tested for influenza.
for a detailed overview in table format. || |
Among the countries reporting on hospitalization of severe influenza cases to the European Centre for Disease Prevention and Control (ECDC), 2 such cases were reported for weeks 17–18 /2013.
For more information on surveillance of confirmed hospitalized influenza, please see ECDC’s Weekly Influenza Surveillance Overview (WISO) at
European Centre for Disease Prevention and Control web site.
Based on the data presented by countries reporting on RSV, the positivity rate peaked in week 52/2012, after which the number of detections has continued to decrease gradually (see Country data and graphs
for individual country data).
Most of the 53 Member States of the WHO European Region monitor influenza activity through surveillance of ILI and/or ARI in primary care clinics, with some countries also conducting hospital-based surveillance for severe disease. Surveillance data in the Region are collected from sentinel and non-sentinel systems. Sentinel data come from a network of designated clinicians who routinely and systematically collect respiratory specimens from ILI, ARI or SARI cases according to standard case definitions. Non-sentinel data come from a variety of other sources, including community outbreaks, general practitioners and hospitals that are not part of the sentinel surveillance system for influenza and may not use a standard case definition for ILI, ARI or SARI.
The EuroFlu bulletin collates and interprets epidemiological and virological data from the different surveillance systems in the Region, to provide information on the timing of the influenza season, the spread of influenza, the prevalence and characteristics of circulating influenza viruses according to influenza type and subtype (A(H3N2) and A(H1N1)pdm09) or lineage (B/Victoria of B/Yamagata), and severity. In addition, influenza viruses are assessed each season for their antigenic and genetic characteristics, to determine the extent of their antigenic and genetic similarity to the viruses included in the seasonal influenza vaccine and the prevalence of mutations that affect pathogenicity or are associated with reduced susceptibility to antiviral drugs.