Epidemiological and virological situation update of the 2010/2011 influenza season in the WHO European Region (Week 40/2010 to Week 03/2011): 10.02.2011

Epidemiological and virological situation update of the 2010/2011 influenza season in the WHO European Region (Week 40/2010 to Week 03/2011) 10 February 2011 Keywords INFLUENZA, HUMAN INFLUENZA SEASON INFLUENZA-LIKE ILLNESS (ILI) ACUTE RESPIRATORY INFECTIONS (ARI) SEVERE ACUTE RESPIRATORY INFECTIONS (SARI) EPIDEMIOLOGY VIROLOGY EUROPE Address requests about publications of the WHO Regional Office for Europe to: Publications WHO Regional Office for Europe Scherfigsvej 8 DK-2100 Copenhagen Ø, Denmark Alternatively, complete an online request form for documentation, health information, or for permission to quote or translate, on the Regional Office web site (http://www.euro.who.int/pubrequest). © World Health Organization 2010 All rights reserved. The Regional Office for Europe of the World Health Organization welcomes requests for permission to reproduce or translate its publications, in part or in full. The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement. The mention of specific companies or of certain manufacturers’ products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. All reasonable precautions have been taken by the World Health Organization to verify the information contained in this publication. However, the published material is being distributed without warranty of any kind, either express or implied. The responsibility for the interpretation and use of the material lies with the reader. In no event shall the World Health Organization be liable for damages arising from its use. The views expressed by authors, editors, or expert groups do not necessarily represent the decisions or the stated policy of the World Health Organization. Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 1 CONTENTS Page Authors…….…………………………………………………………………………………………………………...…….2 Introduction…………………………………………………………………………………………………………...…….3 Current epidemiological overview of the 2010/2011 influenza season……………………………...…3 Sentinel ILI/ARI data ……….……………………………………………………..…………………..…………3 Sentinel data on hospitalised Severe Acute Respiratory Infections (SARI)…….……………….7 Risk factors for severe disease 2010/2011……………………………..………………………….….…..8 Current virological overview of the 2010/2011 influenza season…………….…………………………..9 Sentinel ILI/ARI data …..……………………………………………………….………………………………...9 Non-sentinel virological data ....…………………………………………………….………………………...13 Sentinel data on hospitalised SARI ......………………………………………….…………………….…..14 Antigenic and genetic characterizations ……..……….……………………………………………..…….15 Conclusions………………………………………………………………………………………….……………….….....17 Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 2 Authors WHO Regional Office for Europe Joshua A. Mott, Dmitriy Pereyaslov, Pernille Jorgensen, Caroline Sarah Brown Temporary Advisers to WHO Liana Martiryosan, Tamara Meerhoff Abstract This overview of influenza data from the WHO European Region from weeks 40/2010 through week 3/2011 has been submitted for consideration during the WHO Northern Hemisphere Vaccine Strain Selection Meeting, to be held on 14-17 February, 2011, in Geneva. The 2010/2011 influenza season arrived 8-10 weeks later than the 2009/2010 ‘pandemic’ season in the WHO European Region, but still quite early compared to historical trends. As has been observed in several previous years, the 2010/2011 influenza season appears to be progressing in a West to East fashion across much of Europe. Increases in influenza activity have been accompanied by increases in hospitalised Severe Acute Respiratory infections (SARI) and in severe influenza cases admitted to intensive care units. Pandemic influenza A (H1N1) 2009 viruses are the predominant circulating viruses but in contrast to the 2009/2010 season, there is a higher rate of co-circulation with influenza B viruses and a substantial decrease in the proportion of influenza A(H3N2) viruses. Currently, 98% of antigenically characterized viruses from the 2010/2011 influenza season correspond with the viruses recommended by WHO for inclusion in the 2010- 2011 northern hemisphere influenza vaccine. Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 3 Introduction The WHO Regional Office for Europe, in coordination with the European Centre for Disease Prevention and Control, works with the 53 countries of the WHO European Region to provide a weekly bulletin describing influenza activity in the Region1. Influenza surveillance has traditionally centered on epidemiological data collection for outpatient influenza-like illness (ILI) and acute respiratory infections (ARI) from sentinel sites backed up by laboratory-based generation of virological data. More recently, European Member States are establishing sentinel SARI influenza surveillance systems in order to routinely monitor severe influenza. The laboratory network in Europe consists of WHO-recognized national influenza centres (NICs), many of which participate in the Community Network of Reference Laboratories for Human Influenza in Europe 2, a WHO collaborating centre for reference and research on influenza (WHO CC) and two WHO H5 reference laboratories3. Many of the data included in this report are publicly available at www.euroflu.org, where WHO/Europe publishes a weekly surveillance report in English and Russian that is based on data covering the Region’s total population of 883 million. This overview has been submitted for consideration during the WHO Northern Hemisphere Vaccine Strain Selection Meeting, to be held on 14-17 February, 2011. It complements the data generated by the WHO collaborating centre for reference and research on influenza, NIMR, London, United Kingdom, from analyses performed on influenza viruses provided by European Member States. Current epidemiological overview of the 2010/2011 influenza season Sentinel ILI/ARI data The 2010/2011 influenza season arrived 8-10 weeks later than the 2009/2010 season in the WHO European Region. During 2010/2011, pandemic influenza A (H1N1) 2009 continues to predominate among circulating influenza A viruses in Europe. A noticeable difference from the 2009/2010 season has been the high prevalence Influenza B co-circulation. One measure of the intensity of influenza activity is the percentage of sentinel specimens that test positive for influenza, (represented by the black line on the following graphs, in relation to the right axes). 1 http://www.euroflu.org; http://www.ecdc.europa.eu/en/healthtopics/influenza/epidemiological_data/Pages/Weekly_Influenza_Surveillance_ Overview.aspx 2 http://www.ecdc.europa.eu/en/activities/surveillance/EISN/Pages/AbouttheNetwork_Description.aspx 3 http://www.who.int/csr/disease/influenza/mission/en/index.html; Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 4 To date, during the 2010/2011 influenza season a peak in influenza activity in the European Region was observed during week 52, when over 50% of sentinel specimens in Europe tested positive for influenza. This intensity of influenza activity is similar to that observed during the peak of the 2009/2010 ‘pandemic’ season in Europe. As can be seen in the graphs of recent influenza seasons, the percentage of sentinel specimens testing positive for influenza has been somewhat higher during both the 2010/2011 and the 2009/2010 influenza seasons than during prior recent influenza seasons. This may reflect a greater intensity of influenza circulation resulting from the introduction of a novel virus into naïve human populations, and/or improvements in the sensitivity of laboratory diagnostic methods to detect influenza in use in Europe. Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 5 While the currently observed peak intensity of influenza activity during this season did not occur as early as was experienced during the 2009/2010 season, it has occurred relatively early by European standards. During recent prior influenza seasons, peaks in the intensity of influenza activity have typically been observed between weeks 2 and 6. The current peak during week 52/2010, however, bears some similarity to the 2003/2004 influenza season, which was notable for the circulation of the “Fujian” A (H3N2) virus. It must be noted that the presentation of data for the combined 53 countries of the WHO European Region masks considerable variability in the progression of the influenza season across the Region. As observed in 2008/2009, 2009/2010, and several prior years, the 2010/2011 influenza season appears to be generally progressing in a West to East fashion across much of Europe. This can be seen below in the pattern of observed ILI and ARI consultation rates by country. Currently clinical consultation rates for ILI or ARI vary considerably between countries, and are related to the prevalence of influenza in the population, the prevalence of other respiratory pathogens in the population, and public anxiety regarding influenza. Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 6 a. b. Hospitalisations for severe acute respiratory illness c. Epidemiology of severe influenza virus infections 2. Virological Overview a. Virological detections from sentinel ILI/ARI patients Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 7 ¨ While there are some exceptions, several Western European countries have already reached apparent peaks in ILI and/or ARI activity while other countries farther East are still approaching peaks in clinical consultation rates. Sentinel data on hospitalised Severe Acute Respiratory Infections (SARI) The WHO Regional Office for Europe has been working with European Member States to establish sentinel surveillance systems for hospitalised SARI with the goals of comparing the relative severity of different influenza seasons, and tracking the viruses which specifically cause severe disease. Currently there are 9 countries (Armenia, Georgia, Kazakhstan, Kyrgyzstan, the Republic of Moldova, Romania, the Russian Federation, Serbia, and Ukraine) reporting weekly hospitalised SARI cases, using a standard case definition, to the EuroFlu surveillance platform. The SARI sentinel surveillance systems in these countries generally meet the following two criteria: • SARI is reported from a known, standard, and generally stable number of hospitals on a weekly basis • There is consistent weekly reporting of SARI epidemiological and virological data to the EuroFlu surveillance platform during the 2010/2011 influenza season Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 8 During week 3/2011 data from sentinel systems indicate that SARI hospitalisations have reached the highest reported levels of the 2010/2011 season so far in Georgia, Romania, the Russian Federation and Serbia. In each of these countries, the increase in reported SARI hospitalisations has accompanied concurrent rises in outpatient consultation rates for ILI and/or ARI. Hospitalisations for SARI previously peaked during week 51/2010 in Ukraine and Kyrgyzstan, although reported SARI hospitalisations are again rising in Kyrgyzstan. More detail about the viruses detected from sentinel SARI patients is described in Section 2 below. Risk factors for severe disease 2010/2011 Several countries have reported severe and fatal cases of influenza, and the burden of severe influenza has been sufficient to place considerable strain on critical care services in several locations. This has been notable in the United Kingdom and Ireland but reported in other countries as well. While most critical and fatal influenza cases have been associated with influenza A (H1N1) 2009 virus infections, a smaller number of severe influenza B virus infections are also being reported. The age and underlying risk profile of these severe cases appears similar to that observed during the 2009/2010 ‘pandemic’ influenza season4. As of week 03/2011, the United Kingdom reported that 320 (92%) of 347 fatal influenza cases were associated with H1N1 (2009) infection, seven with un-subtyped influenza A and 20 (6%) with influenza B infection. Reported deaths have been mainly in younger adults and children. Among the 306 cases with information on age: ten (3%) have been less than 5 years; 14 (5%) from 5 to 14 years; 217 (71%) from 4 See http://www.euro.who.int/en/what-we-do/health-topics/diseases-and- conditions/influenza/publications/2012/influenza-h1n1-2009-key-issues-for-case-management Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 9 15 to 64 years and 65 (21%) older than 64 years of age. One hundred and eighty-four of 252 fatal cases with available information (73%) were in defined clinical risk groups for vaccination. The leading reported clinical risk factors for those with information were underlying respiratory disease including asthma (n=49) and immunosuppression (n=43). Of cases with available information on immunisation history, 82 of 108 (76%) cases had not received the 2010/11 trivalent influenza vaccine this season. Thirty-nine of 41 (95%) of cases with available information had not received the monovalent pandemic influenza vaccine last season.i In Ireland sixty‐nine of 98 (70.4%) hospitalised influenza cases in critical care have underlying medical conditions, 62 adults and seven paediatric cases. The underlying medical conditions include: chronic respiratory disease, chronic heart disease, immunosuppression, pregnancy, metabolic disorders and morbid obesity. Age-specific rates of ICU admissions in Ireland appear highest in the youngest ages, and then increase again in adulthood with a peak in the 55-64 year age group.ii Current virological overview of the 2010/2011 influenza season The tables that follow describe the influenza viruses that have been circulating in the WHO European Region during the 2010/2011 influenza season. Virological data from sentinel ILI/ARI surveillance systems, non-sentinel virological surveillance systems, and sentinel surveillance systems for hospitalised SARI are presented in turn. Sentinel ILI/ARI data Tables 1-3 present the number and percentage of sentinel ILI/ARI specimens testing positive for influenza, by type of influenza, and month of the current influenza season. Table 1 presents the data for the entire WHO European Region and Tables 2 and 3 present stratified data for i) countries of Eastern Europe, namely the Caucasus, Central Asia and the Russian Federation, and ii) countries of Western, Central, and South Eastern Europe, respectively. The specific countries included in each of these groupings may be found in the endnote to this document. Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 10 Table 1: Number and percentage of sentinel ILI/ARI specimens testing positive for influenza, by type of influenza, and month, WHO European Region Table 2: Number and percentage of sentinel ILI/ARI specimens testing positive for influenza, by type of influenza, and month, Caucasus, Central Asia and Russian Federation iii Table 3: Number and percentage of sentinel ILI/ARI specimens testing positive for influenza, by type of influenza, and month, Western, Central, and South Eastern Europe iv Month Number of sentinel specimens tested Number (%) of sentinel specimens positive for influenza Number (%) of sentinel specimens positive for influenza A Number (%) of sentinel specimens positive for influenza B October, 2010 2605 51 (2.0%) 22 (0.8%) 29 (1.1%) November, 2010 2912 146 (5.0%) 76 (2.6%) 70 (2.4% December, 2010 7562 2778 (36.7%) 1959 (25.9%) 819 (10.8%) January, 2011 9759 4562 (46.7%) 3183 (32.6%) 1379 (14.1%) Total 22838 7537 (33.0%) 5240 (22.9%) 2297 (10.1%) Month Number of sentinel specimens tested Number (%) of sentinel specimens positive for influenza Number (%) of sentinel specimens positive for influenza A Number (%) of sentinel specimens positive for influenza B October, 2010 346 0 (0.0%) 0 (0.0%) 0 (0.0%) November, 2010 409 6 (1.5%) 4 (1.0%) 2 (0.5%) December, 2010 430 25 (5.8%) 7 (1.6%) 18 (4.2%) January, 2011 304 84 (27.6%) 55 (18.1%) 29 (9.5%) Total 1489 115 (7.7%) 66 (4.4%) 49 (3.3%) Month Number of sentinel specimens tested Number (%) of sentinel specimens positive for influenza Number (%) of sentinel specimens positive for influenza A Number (%) of sentinel specimens positive for influenza B October, 2010 2259 51 (2.3%) 22 (10%) 29 (1.3%) November, 2010 2503 140 (5.6%) 72 (2.9%) 68 (2.7%) December, 2010 7132 2753 (38.6%) 1952 (27.4%) 801 (11.2%) January, 2011 9455 4478 (47.4%) 3128 (33.1%) 1350 (14.3%) Total 21349 7422 (34.8%) 5174 (24.2%) 2248 (10.5%) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 11 Notable increases in the intensity of both influenza A and B circulation occurred during December 2010, and then further increased in January 2011. Consistent with the epidemiological data on ILI/ARI consultation rates, a pronounced start of the influenza season was observed in December 2010 in the countries of Western, Central, and South Eastern Europe and in January 2011 in the Caucasus, Central Asia, and the Russian Federation. Although more sentinel specimens have been collected and tested in the countries of Western, Central, and South Eastern Europe, a relative predominance of influenza A over influenza B is being observed across the WHO European Region. Tables 4-6 further describe the subtypes of influenza viruses collected from sentinel ILI/ARI patients. It can be seen that there is a growing predominance of pandemic influenza A (H1N1) 2009 viruses, accompanied by a notable decrease in the relative proportion of influenza A (H3N2) viruses among circulating influenza A viruses. A particular increase in the relative circulation of influenza A (H1N1) 2009 viruses can be seen in the month of January 2011 in the Caucasus, Central Asia, and the Russian Federation. Influenza B viruses continue to co-circulate with influenza A viruses in the Region. Across the Region, 94% of influenza B viruses, for which lineage is known, belong to the B-Victoria lineage. No seasonal influenza A (H1N1) viruses have been detected in sentinel specimens. Table 4: Type and sub-type of influenza viruses collected from sentinel ILI/ARI patients, by month, WHO European Region * There were 299 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 282 (94%) were B‐Victoria lineage and 17 (6%) were B‐Yamagata lineage. October November December January TOTAL Number of sentinel specimens tested for influenza 2605 2912 7562 9759 22838 Number and percentage of tested specimens positive for influenza 51 (2.0%) 146 (5.0%) 2778 (36.7%) 4562 (46.7%) 7537 (33.0%) Number (% of all influenza) positive for influenza A 22 (43.1%) 76 (52.1%) 1959 (70.5%) 3183 (69.8%) 5240 (69.5%) Number of influenza A viruses sub- typed 20 73 1803 2921 4817 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 11 (55.0%) 56 (76.7%) 1660 (92.1%) 2714 (92.9%) 4441 (92.2%) Number (%) of subtyped A positive for influenza A (H3) 9 (45.0%) 17 (23.3%) 143 (7.9%) 207 (7.1%) 376 (7.8%) Number (%) of subtyped A positive for influenza A (H1) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Number (%) of all influenza positive for influenza B * 29 (56.9) 70 (47.9) 819 (29.5) 1379 (30.2) 2297 (30.5) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 12 Table 5: Type and sub-type of influenza viruses collected from sentinel ILI/ARI patients, by month, Caucasus, Central Asia and the Russian Federation * There were 18 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 17 (94%) were B‐Victoria lineage and 1 (6%) were B‐Yamagata lineage. Table 6: Type and sub-type of influenza viruses collected from sentinel ILI/ARI patients, by month, Western, Central, and South Eastern Europe * There were 281 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 265 (94%) were B‐Victoria lineage and 16 (6%) were B‐Yamagata lineage. October November December January TOTAL Number of sentinel specimens tested for influenza 346 409 430 304 1489 Number and percentage of tested specimens positive for influenza 0 (0.0%) 6 (1.5%) 25 (5.8%) 84 (27.6%) 115 (7.7%) Number (%) of all influenza positive for influenza A 0 (0.0%) 4 (66.7%) 7(28.0%) 55 (65.5%) 66 (57.4%) Number of influenza A viruses sub- typed 0 3 6 44 53 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 0 (0.0%) 1 (33.3%) 2 (33.3%) 42 (95.5%) 45 (84.9%) Number (%) of subtyped A positive for influenza A (H3) 0 (0.0%) 2 (66.7%) 4 (66.7%) 2 (4.5%) 8 (15.1%) Number (%) of subtyped A positive for influenza A (H1) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Number (%) of all influenza positive for influenza B * 0 (0.0%) 2 (33.3%) 18 (72.0%) 29 (34.5%) 49 (42.6%) October November December January TOTAL Number of sentinel specimens tested for influenza 2259 2503 7132 9455 21349 Number and percentage of tested specimens positive for influenza 51 (2.3%) 140 (5.6%) 2753 (38.6%) 4478 (47.4%) 7422 (34.8%) Number (%) of all influenza positive for influenza A 22 (43.1%) 72 (51.4%) 1952 (70.9%) 3128 (69.9%) 5174 (69.7%) Number of influenza A viruses sub- typed 20 70 1797 2877 4764 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 11 (55.0%) 55 (78.6%) 1658 (92.3%) 2672 (92.9%) 4396 (92.3%) Number (%) of subtyped A positive for influenza A (H3) 9 (45.0%) 15 (21.4%) 139 (7.7%) 205 (7.1%) 368 (7.7%) Number (%) of subtyped A positive for influenza A (H1) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Number (%) of all influenza positive for influenza B * 29 (56.9%) 68 (48.6%) 801 (29.1%) 1350 (30.1%) 2248 (30.3%) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 13 Non-sentinel virological data In order to more fully describe the influenza viruses detected during 2010/2011 across the WHO European Region, Tables 7-9 present the type and sub-type of influenza viruses collected from non- sentinel sources (laboratory tests resulting from routine diagnostic requests from clinicians, etc..). Table 7: Type and sub-type of influenza viruses collected from non-sentinel sources, by month, WHO European Region * There were 299 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 282 (94%) were B‐Victoria lineage and 17 (6%) were B‐Yamagata lineage. Table 8: Type and sub-type of influenza viruses collected from non-sentinel sources, by month, Caucasus, Central Asia and the Russian Federation * There were 18 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 17 (94%) were B‐Victoria lineage and 1 (6%) were B‐Yamagata lineage. October November December January TOTAL Number of tested specimens positive for influenza 81 321 7898 14785 23085 Number (%) of all influenza positive for influenza A 54 (66.7%) 165 (51.4%) 5456(69.1%) 10410 (70.6%) 16115 (69.8%) Number of influenza A viruses sub- typed 36 87 2674 6310 9107 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 17 (47.2%) 53 (60.9%) 2516 (94.1%) 6174 (97.5%) 8760 (96.2%) Number (%) of subtyped A positive for influenza A (H3) 18 (50.0%) 34 (39.1%) 158 (5.9%) 136 (2.2%) 346 (3.8%) Number (%) of subtyped A positive for influenza A (H1) 1 (2.8%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 1 (0.0%) Number (%) of all influenza positive for influenza B * 27 (33.3%) 156 (48.6%) 2442 (30.9%) 4345 (29.4%) 6970 (30.2%) October November December January TOTAL Number of tested specimens positive for influenza 26 58 466 1059 1609 Number (%) of all influenza positive for influenza A 14 (53.8%) 24 (41.4%) 155 (33.3%) 673 (63.6%) 866 (53.8%) Number of influenza A viruses sub- typed 13 21 137 644 815 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 2 (15.4%) 8 (38.1%) 86 (62.8%) 611 (94.9%) 707 (86.7%) Number (%) of subtyped A positive for influenza A (H3) 10 (76.9%) 13 (61.9%) 51 (37.2%) 33 (5.1%) 107 (13.1%) Number (%) of subtyped A positive for influenza A (H1) 1 (7.7%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 1 (0.1%) Number (%) of all influenza positive for influenza B * 12 (46.2%) 34 (58.6%) 311 (66.7%) 386 (36.4%) 743 (46.2%) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 14 Table 9: Type and sub-type of influenza viruses collected from non-sentinel sources, by month, Western, Central and Eastern Europe * There were 281 influenza B viruses for which the influenza lineage was known. Of these influenza B viruses, 265 (94%) were B‐Victoria lineage and 16 (6%) were B‐Yamagata lineage. The data collected from non-sentinel sources present a pattern similar to that observed in the sentinel ILI/ARI surveillance data. A notable increase in the predominance of influenza A(H1N1) 2009 among influenza A viruses can be observed from October 2010 to January 2011. The non-sentinel surveillance data also highlight the increase in the relative circulation of influenza A viruses compared to influenza B viruses during the month of January 2011 in the Caucasus, Central Asia, and the Russian Federation. A single seasonal influenza A (H1N1) virus was detected in a non-sentinel specimen in October 2010. No seasonal influenza A (H1N1) viruses have been detected in the WHO European Region since that time. Sentinel data on hospitalised SARI Currently there are nine countries that provide sentinel virological data from hospital-based SARI surveillance to the EuroFlu platform. Table 10 presents the type and sub-type of influenza viruses collected from SARI patients. During week 3/2011, 20% of hospitalised SARI patients tested positive for influenza. During this week the relative distribution of influenza types (63% influenza A and 37% influenza B), and subtypes (96% influenza A (H1N1) 2009 and 4% influenza A (H3N2)) in SARI patients appeared similar to what was observed from other sentinel and non-sentinel data sources. The striking difference in the proportion of influenza A to influenza B viruses during week 3/2011 when compared to cumulative data from week 40/2010 to week 3/2011 likely reflects the recent shift in the relative circulation of influenza B to influenza A in the Caucasus, Central Asia, and the Russian Federation—as many countries that are implementing SARI surveillance are located in this part of the WHO European Region. October November December January TOTAL Number of tested specimens positive for influenza 55 263 7432 13726 21476 Number (%) of all influenza positive for influenza A 40 (72.7%) 141 (53.6%) 5301(71.3%) 9767 (71.2%) 15249 (71.0%) Number of influenza A viruses sub- typed 23 66 2537 5666 8292 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 15 (65.2%) 45 (68.2%) 2430 (95.8%) 5563 (98.2%) 8053 (97.1%) Number (%) of subtyped A positive for influenza A (H3) 8 (34.8%) 21 (31.8%) 107 (4.2%) 103 (1.8%) 239 (2.9%) Number (%) of subtyped A positive for influenza A (H1) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) Number (%) of all influenza positive for influenza B * 15 (27.3%) 122 (46.4%) 2131 (28.7%) 3959 (28.8%) 6227 (29.0%) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 15 Table 10: Type and sub-type of influenza viruses collected from hospitalised SARI patients, week 40/2010 to week 3/2011, WHO European Region v * There were 19 influenza B viruses for which the influenza lineage was known. All 19 were of the B‐Victoria lineage. Antigenic and Genetic Characterizations The antigenic and genetic characterizations performed on influenza isolates by NICs in the WHO European Region are presented in Tables 11 and 12, respectively. Of the 465 pandemic influenza A (H1) viruses that have been antigenically characterized during the 2010/2011 influenza season, 100% are antigenically similar to pandemic A/California/7/2009 (H1N1)-like viruses. Of the 79 influenza A (H3N2) viruses that have been characterized, 100% are antigenically similar to) A/Perth/16/2009 (H3N2)-like viruses. Of the 279 influenza B viruses that have been antigenically characterized, 262 (94%) are B/Brisbane/60/2008-like (B/Victoria/2/87 lineage) and 17 (6%) are B/Florida/4/2006-like (B/Yamagata/16/88 lineage). All 17 viruses from the influenza B-Yamagata lineage were reported by Western, Central, and South Eastern European countries. Taken together, 98% of antigenically characterized viruses were similar to 2010-2011 northern hemisphere influenza vaccine strains. Genetic characterization of 109 circulating influenza viruses suggest that all influenza A (H1) viruses are in the pandemic cluster represented by the current vaccine strain A/California/7/2009 A (H1N1). The influenza A (H3) that have been genetically characterized are in the clades represented by A/Perth/16/2009, A/Victoria/208/2009, and the A/Victoria/208/2009 - A/Hong Kong/2121/2010 subgroup. Influenza B viruses are in the clades represented by B/Bangladesh/3333/2007 and B/Brisbane/60/2008. Week 3/2011 Cumulative, week 40/2010 to week 3/2011 Number of sentinel SARI specimens tested for influenza 233 1766 Number and percentage of tested SARI specimens positive for influenza 46 (19.7%) 272 (15.4%) Number (%) of all influenza positive for influenza A 29 (63%) 79 (29%) Number of influenza A viruses sub-typed 24 65 Number (%) of subtyped A positive for pandemic influenza A (H1) 2009 23 (96%) 57 (86%) Number (%) of subtyped A positive for influenza A (H3) 1 (4%) 8 (14%) Number (%) of subtyped A positive for influenza A (H1) 0 (0%) 0 (0%) Number (%) of all influenza positive for influenza B * 17 (37%) 193 (71%) Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 16 Table 11: Antigenic characterization of influenza isolates from the WHO European Region * Included in the WHO recommended composition of influenza virus vaccines for use in the 2010‐2011 northern hemisphere influenza season (http://www.who.int/csr/disease/influenza/recommendations2010_11north/en/index.html) # Included in the WHO recommended composition of influenza virus vaccines for use in the 2011 southern hemisphere influenza season (http://www.who.int/csr/disease/influenza/recommendations2011south/en/index.html). Table 12: Genetic characterization of influenza isolates from the WHO European Region WHO European Region Caucasus, Central Asia and Russian Federation Western, Central, and South Eastern, Europe Viruses Number % Number % Number % A(H1)pandemic A/California/7/2009 (H1N1)-like*# 465 56.5 14 50.0 451 56.7 A(H1) A/Brisbane/59/2007 (H1N1)‐like 0 0 0 0 0 0 A(H3) A/Perth/16/2009 (H3N2)-like*# 79 9.6 9 32.1 70 8.8 B/Florida/4/2006‐like (B/Yamagata/16/88 lineage) 17 2.1 0 0 17 2.1 B/Bangladesh/3333/2007‐like (B/Yamagata/16/88 lineage) 0 0 0 0 0 0 B/Brisbane/60/2008-like (B/Victoria/2/87 lineage)*# 262 31.8 5 17.9 257 32.3 Grand Total 823 100.0 28 100.0 795 100.0 Virus Characterization Number A(H1)pandemic cluster repr. A/California/7/2009 A(H1N1)pandemic 70 A(H1)pandemic cluster repr. A/Christchurch/16/2010 4 A(H1)pandemic cluster repr. A/Hong Kong/2213/2010 8 A(H1) clade 2B ‐ repr. A/Brisbane/59/2007 0 A(H3) clade repr. A/Brisbane/10/2007 0 A(H3) clade repr. A/Perth/16/2009 7 A(H3) clade repr. A/Victoria/208/2009 2 A(H3) clade repr. A/Victoria/208/2009 ‐ A/Hong Kong/2121/2010 subgroup 11 B(Yam) lineage ‐ clade repr. B/Bangladesh/3333/2007 6 B(Yam) lineage ‐ clade repr. B/Brisbane/3/2007 0 B(Yam) lineage ‐ clade repr. B/Florida/4/2006 0 B(Vic) lineage ‐ clade repr. B/Brisbane/60/2008 1 B(Vic) lineage ‐ clade repr. B/Bolivia/104/2010 0 Grand Total 109 Epidemiological and virological situation update of 2010/2011 influenza season (WHO European Region) page 17 Conclusions The 2010/2011 influenza season arrived 8-10 weeks later than the 2009/2010 ‘pandemic’ season in the WHO European Region, but still quite early compared to historical trends. The percentage of sentinel specimens currently testing positive for influenza in the Region is similar to that observed during the peak of the 2009/2010 season. As has been observed in several previous years, the 2010/2011 influenza season appears to be progressing in a West to East fashion across much of Europe. Several Western European countries have reached peaks in ILI or ARI activity, and in the percentage of sentinel specimens testing positive for influenza. However other countries are still approaching peaks in influenza activity. Increases in influenza activity have been accompanied by increases in hospitalised SARI and severe influenza cases; particularly those associated with pandemic A (H1N1) 2009 virus infections. While this has placed a strain on critical care resources in several locations, the age and underlying risk profile of the severe cases appears similar to what was observed during the 2009/2010 ‘pandemic’ season. During recent weeks the relative distribution of influenza viruses in SARI cases from sentinel hospitals appears similar to what has been observed in other sentinel and non-sentinel surveillance systems. Relative to the increased circulation of pandemic influenza A (H1N1) 2009 viruses, the proportion of influenza A(H3N2) viruses has substantially decreased during the course of the 2010/2011 influenza season. While influenza B viruses continue to co-circulate with influenza A viruses, their relative presence has declined somewhat in countries where there are currently increasing numbers of influenza (H1N1) 2009 viruses in circulation. This has been particularly notable during January 2011 in the Caucasus, Central Asia and the Russian Federation. Currently, 98% of antigenically characterized viruses from the 2010/2011 influenza season are similar to the 2010-2011 northern hemisphere influenza vaccine strains. i http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1294740643915 (last accessed 1 February, 2011) ii http://www.hpsc.ie/hpsc/A- Z/Respiratory/Influenza/SeasonalInfluenza/Surveillance/InfluenzaSurveillanceReports/20102011Season/File,11977, en.pdf (last accessed 1 February, 2011) iii Armenia, Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan, Russian Federation, Tajikistan, Uzbekistan, Turkmenistan iv Albania, Austria, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Latvia, Lithuania, Luxembourg, Malta, Montenegro, Netherlands, United Kingdom, Norway, Poland, Portugal, Republic of Moldova, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, The former Yugoslav Republic of Macedonia, Turkey, Ukraine v Countries currently meeting the minimum reporting criteria and who are submitting sentinel SARI virological data to EuroFlu include Armenia, Georgia, Kazakhstan, Kyrgyzstan, Republic of Moldova, Romania, Russian Federation, and Ukraine