[Source: EuroFlu, full page: (LINK). Edited.]

EuroFlu - Weekly Electronic Bulletin - Week 13 : 24/03/2014-30/03/2014 - 04 April 2014, Issue No. 524

Influenza activity returns to pre-season levels in Europe

Summary, week 13/2014
  • Recent declines in clinical indicators have been observed in nearly all countries in the WHO European Region, and influenza activity returned to pre-season levels or below seasonal thresholds in the majority.
  • The percentages of sentinel influenza-like illness (ILI), acute respiratory infection (ARI) and severe acute respiratory infection (SARI) specimens testing positive for influenza, have also declined during recent weeks.
  • Influenza A(H1N1)pdm09 and A(H3N2) viruses continue to co-circulate in the Region, with very few influenza B detections reported during this season.

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.

Virological surveillance for influenza

During week 13/2014, both the total number of specimens tested for influenza and the influenza positivity rate continued to decline, with a slightly increasing number of influenza B detections in comparison with previous weeks.

11 189 specimens from sentinel and non-sentinel sources were tested for influenza, 1797 (16%) of which were positive: 1594 (89%) for influenza A and 203 (11%) for influenza B (Fig. 1 and 2).


Influenza A has remained the dominant virus type in circulation across the Region since the start of weekly monitoring in week 40/2013.
Of the 948 influenza A viruses that were subtyped during week 13/2014, 418 (44%) were A(H1N1)pdm09 and 530 (56%) A(H3N2) (Fig. 2a).

Since week 40/2013, sentinel and non-sentinel sources have yielded 40 088 influenza detections: 38 182 (95%) were influenza A and 1906 (5%) influenza B viruses (Fig. 2b).

Of the 26 546 influenza A viruses that have been subtyped, 15 459 (58%) were A(H1N1)pdm09 and 11 087 (42%) were A(H3N2).

In addition, the lineage of 172 influenza B viruses has been determined: 158 (92%) belonged to the B/Yamagata lineage (the lineage of the B virus recommended by WHO for inclusion in trivalent seasonal influenza vaccines) and 14 (8%) to the B/Victoria lineage.



With the decline of influenza activity in the Region, fewer countries than in previous weeks are reporting on dominant influenza type.

Of the 41 countries supplying such data, only 22 reported influenza A as dominant in week 13/2014.

Turkey was the only country reporting influenza B as dominant, but the number of detections was low (Map 1 and country table).

Of countries providing data on dominant subtypes, influenza A(H3N2) was reported as dominant in 12 countries (Belgium, Croatia, Germany, Hungary, Ireland, Lithuania, Romania, the Russian Federation, Slovenia, Spain, Switzerland and Ukraine), while only 4 countries (Denmark, Greece, Norway and the United Kingdom (Scotland)) reported A(H1N1)pdm09 as dominant.

3 countries (France, Italy and Latvia) reported A(H1N1)pdm09 and A(H3N2) as co-dominant.

Virus strain characterizations

Circulating influenza viruses are assessed each season for their antigenic and genetic characteristics, to determine the extent of their antigenic similarity to the viruses included in the seasonal influenza vaccine, and determine the prevalence of mutations that affect pathogenicity or are associated with susceptibility to antiviral drugs.

For the 2013/2014 northern hemisphere influenza season, WHO recommended inclusion of A/California/7/2009 (H1N1)pdm09-like, A/Texas/50/2012 (H3N2)-like and B/Massachusetts/2/2012-like (Yamagata lineage) viruses in vaccines (see the WHO headquarters web site).

The WHO Consultation on the Composition of Influenza Virus Vaccines for the Northern Hemisphere 2014?2015 took place in week 7/2014, and the WHO expert group recommended no change from the vaccine composition for the 2013?2014 season. (see the WHO headquarters web site).

Since week 40/2013, 1565 influenza viruses characterized antigenically by 13 countries (the Czech Republic, Denmark, Finland, Germany, Ireland, Latvia, the Netherlands, Portugal, Romania, the Russian Federation, Slovakia, Switzerland and the United Kingdom (England, Scotland)) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine (Fig. 3).

14 countries (Belgium, the Czech Republic, Denmark, Finland, Germany, Greece, Ireland, the Netherlands, Norway, Portugal, the Russian Federation, Spain, Sweden and Switzerland) have characterized 820 influenza viruses genetically (Fig. 4).


# Included in the WHO-recommended composition of influenza virus vaccines for use in the 2013/2014 northern hemisphere influenza season.

* Included in the WHO-recommended composition of influenza virus vaccines for use in the 2014 southern hemisphere influenza season.

Monitoring of susceptibility to antiviral drugs

Since week 40/2013, 9 countries (Greece, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the Russian Federation and the United Kingdom (England)) have screened 885 viruses for susceptibility to the neuraminidase inhibitors oseltamivir and zanamivir.

Of the 740 A(H1N1)pdm09 viruses tested, 731 showed susceptibility to both drugs; 9 viruses carrying the neuraminidase H275Y amino acid substitution, causing resistance to oseltamivir, were identified.

Of these 9 viruses, 8 were detected in the United Kingdom in hospitalized patients, most of whom were treated with neuraminidase inhibitors, and 1 virus from Switzerland was detected in a hospitalized immunocompromised patient treated with oseltamivir.

Of the 204 influenza A(H3N2) viruses tested, 203 showed susceptibility to both drugs.

The remaining virus, detected in the United Kingdom in a hospitalized immunocompromised patient treated with oseltamivir, carried the neuraminidase E119V amino acid substitution, and showed reduced inhibition by oseltamivir but normal inhibition by zanamivir.

All 38 influenza B viruses tested showed susceptibility to both oseltamivir and zanamivir.

So far, there is no indication of increased resistance to the neuraminidase inhibitors during the winter of 2013?2014. All 130 influenza A(H1N1)pdm09 and 85 influenza A(H3N2) viruses screened for susceptibility to adamantanes were found to be resistant.

Outpatient surveillance for influenza-like illness (ILI) and/or acute respiratory infection (ARI)

During week 13/2014, most European countries reported low-intensity influenza activity (Map 2), with only 3 countries reporting increasing trends (Map 4). As to geographic spread, influenza activity was mainly sporadic in the majority of countries (Map 3).

During week 13/2014, consultation rates continued to decline in most countries in the Region. Of the 22 countries with established national thresholds, the rates returned to or were below the threshold levels in the majority. In a number of northern and western countries (the Czech Republic, Denmark, Germany, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Slovakia, Switzerland and the United Kingdom (England)), consultation rates have remained very low since the beginning of the season (mostly below the threshold) and much lower than last season.


The percentage of positive sentinel ILI/ARI specimens decreased in comparison with the previous week and remained much lower than at the same period last season (Fig. 5).


During week 13/2014, 187 (18%) of the 1017 specimens collected from sentinel sources tested positive for influenza virus; the majority were influenza A(H3N2) (Fig. 6a), similar to the previous weeks. The number of influenza B detections remained low but has increased slightly over recent weeks. Click here for a detailed overview in a table format.


Hospital surveillance for SARI

For sentinel surveillance of severe disease due to influenza, in week 13/2014 the number of SARI hospitalizations continued to decrease, with most cases reported in those aged 0?4 years. The percentage of SARI patients who tested positive for influenza remained at the same level as the previous week (Fig. 7).


During week 13/2014, 38 (23%) of the 162 SARI samples collected from sentinel surveillance in Armenia, Belarus, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, Slovakia and Ukraine tested positive for influenza A, the majority being A(H3N2) (Fig. 8a), in line with the results of sentinel ILI/ARI surveillance. Click here for a detailed overview in table format.


For week 13/2014, 5 countries (France, Ireland, Romania, Spain and the United Kingdom) reported 92 hospitalized laboratory-confirmed influenza cases . Influenza A virus was detected in 89 cases and influenza B virus in 3.

Since week 40/2013, 7 countries have reported 4390 hospitalized, laboratory-confirmed influenza cases: 4339 (99%) were related to influenza virus type A infection and 51 (1%) to type B . Of 2956 subtyped influenza A viruses, 2209 (75%) were A(H1)pdm09 and 747 (25%) were A(H3). A higher proportion of A(H1)pdm09 viruses has been detected in patients in intensive care units (ICUs) (1265 out of 1481 subtyped: 85%) than in other hospitalized patients (944 out of 1475 subtyped: 64%).

5 countries reported a total of 368 fatal cases: 365 (99%) were associated with influenza virus type A infection and 3 (1%) with type B. Of 269 influenza A viruses subtyped from fatal cases, 218 (81%) were A(H1)pdm09 and 51 (19%) were A(H3).

The results from SARI surveillance at sentinel hospitals reported to the WHO Regional Office for Europe (EuroFlu) and hospitalized laboratory-confirmed influenza cases reported to the European Centre for Disease Prevention and Control (ECDC) differ in that the former include a higher proportion of influenza A(H3N2) and a lower proportion of influenza A(H1N1)pdm09 than the latter. This pattern is most likely due to the circulation of the different influenza virus subtypes in countries.

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.

Respiratory syncytial virus (RSV)

Based on the data reported by countries on RSV, detections peaked in week 50/2013 and have decreased in all the reporting countries since. This represents a slightly later start than in the previous season (see Country data and graphs for individual country data).

EuroMOMO (European Mortality Monitoring Project)

EuroMOMO is a project set up to develop and operate a routine public health mortality monitoring system to detect and measure, on a real-time basis, excess deaths related to influenza and other possible public health threats across 20 European Union (EU) countries.

Pooled analysis of week data for 13/2014 showed that all-cause mortality was within the normal range for all reporting countries. Results of pooled analysis may vary, depending on which countries are included in the weekly analysis.

For more information about the EUROMOMO mortality monitoring system please click here.