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Global Influenza Epidemiology Overview for Europe, with particular emphasis on Southern Hemisphere Temperate Countries - week 40 (edited)

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    Re: Global Influenza Epidemiology Overview for Europe, with particular emphasis on Southern Hemisphere Temperate Countries - week 40 (edited)

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  • Global Influenza Epidemiology Overview for Europe, with particular emphasis on Southern Hemisphere Temperate Countries - week 40 (edited)

    Global Influenza Epidemiology Overview for Europe, with particular emphasis on Southern Hemisphere Temperate Countries - week 40 (edited)

    [Source: European Centre for Disease Prevention and Control (ECDC), full page (LINK). Extracts, edited.]

    Global Influenza Epidemiology Overview for Europe, with particular emphasis on Southern Hemisphere Temperate Countries - week 40

    14 Oct 2010

    Note the Epidemiology for Europe is covered in the Weekly Influenza Surveillance Overview (WISO)

    The world is post pandemic that is, meaning that according to the WHO criteria ?Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance.? Post pandemic seasonal influenza can be different from the preceding influenza and therefore careful attention has to be paid to what is happening with the ?new? seasonal influenza pattern. This is highlighted in a recent editorial by ECDC.

    Southern Hemisphere Temperate Countries

    Following the recommendations of an Advisory Forum group that oversaw the development of ?ECDC?s Forward Look Risk Assessment ? the experiences with influenza in the temperate countries of the Southern Hemisphere are being monitored especially carefully by ECDC during the Northern Hemisphere summer and autumn. The special interest this year is because these are the first countries to experience a second winter of transmission with the 2009 pandemic virus. Hence they give one, maybe the best indication of what Europe can expect in its winter of 2010/2011. This is being done using epidemic intelligence techniques consulting routine and non-routine published sources in the five temperate Southern Hemisphere countries with developed long-term epidemiological and virological surveillance systems: Argentina, Australia, Chile, New Zealand and South Africa.

    Sources of Epidemic Intelligence Information for Southern Hemisphere Temperate Countries:

    As Argentina and South Africa have already ceased publishing weekly reports on their Ministry of Health websites this update focuses especially on recent information from Chile, Australia and New Zealand (see graphs below).

    As in most years, seasonal influenza transmission started to rise in the Southern Hemisphere temperate countries after May and June (see Figures below). However, the patterns of transmission and the viruses responsible have been diverse, much more diverse than in the pandemic winter of 2009 (Table).

    South Africa experienced low levels of influenza like illness H3N2 and type B viruses, and hardly any influenza A(H1N1) . In contrast, in the other four countries (Argentina, Australia, Chile and New Zealand) the pandemic influenza A(H1N1) strain initially predominated but with some A(H3N2) and B viruses. As elsewhere in the world there have been none of the previous seasonal A(H1N1) viruses.

    Chile is the only one of the five countries that tests also routinely for and reports on respiratory syncytial viruses (RSV) and these viruses resulted in early epidemics of respiratory infection in children (see figures for Chile). With the exception of New Zealand, all the other countries have reported levels of transmission in the community (as reflected in consultations) and hospitalisations, which were quantitatively lower than in the last 2009 Southern Hemisphere winter when those countries experienced pandemic waves.

    Now Argentina, Australia, Chile and South Africa are not reporting many cases of severe disease associated with influenza and generally neither the health services nor the critical services are stressed i.e. the pattern of illness is looking more like seasonal influenza than the pandemic pattern seen in the winter of 2009 in those countries.

    The two Southern Hemisphere countries that experienced a late season rising of ILI consultations and virological reports (Australia and Chile) during the last month are now experiencing decreasing trend indicating that their influenza seasons are coming to an end (see figures below).


    In the reporting period 18th-24th September 2010 (week 38), data from a number of surveillance systems indicates that, although influenza activity rose late in the season, the levels of overall national rates of ILI consultations in primary care have decreased of late reaching similar levels to those observed in 2007 and 2008. There remains considerable heterogeneity across the country and over all the proportion of sentinel respiratory samples testing positive for influenza virus has remains 17%, still a figure considerably higher than earlier in the season.

    The majority (69%) of recent influenza virus isolations have been characterized as H1N1 2009, though seasonal H3N2 and B viruses have also been detected. It will be important to determine what viruses are driving these late epidemics.

    In 2010 the age distribution of influenza laboratory reports were intermediate between those of 2008 and 2009 being relatively consistent across all age groups but decreasing with increasing age so that as in both the pandemic winter and 2010 older people were under-represented at least in laboratory reports (see Figure).

    To date there are few deaths reported associated with influenza, predominately (15 / 18) people with underlying health conditions. There are no data indicating to what extent the transmission has been affected by by immunisation in 2009 and 2010 with first pandemic and then seasonal influenza vaccines in Australia. However there are informal reports that seasonal vaccines were used extensively.


    In the latest influenza report from Chile (reporting from 26th September ? 02nd October 2010) it is noted that the number of respiratory consultations is now starting to decrease. RSV circulation, which was responsible for early local epidemics in children, has especially decreased during the last weeks accounting now for only 22% of the total of viruses, followed by influenza B and para-influenza viruses.

    In addition, the co-circulation of 2009 pandemic influenza A(H1N1) and H3N2 viruses continues with the latter becoming more important (55%); the proportion of all influenza viruses accounted for by the A(H3N2) viruses is now higher than that of 2009 pandemic influenza A(H1N1) virus.

    New Zealand:

    This country has also shown an unusual pattern of influenza infection this winter. The Ministry of Health reported a national rate for influenza-like illness (ILI) during the last two weeks has continued to decrease and now is lower than the baseline level and to the levels observed during 2009 and 2008 (see New Zealand figure below).

    However, overall influenza activity (as indicated by rates of ILI, hospitalizations and absenteeism) has been notably uneven geographically. The New Zealand Ministry of Health reports that transmission has been focally intense in some areas, even higher for those areas than in the pandemic winter.

    However overall rates of ILI and numbers of severe and fatal cases in New Zealand remain below the levels seen during the winter 2009 pandemic wave and the current seasonal epidemic shows evidence that they have passed its peak.

    Table - Influenza Pattern in Five Southern Hemisphere Temperate Countries in their 2010 Winter

    [Country - Community Epidemiology - Virology]
    • Argentina (few data) - Lower observed rates than in 2009 ? Fewer severe cases - Mostly A(H1N1)
    • Australia - Lower observed rates than in 2009 - Fewer severe cases Late season rise due to a mix of viruses A(H1N1) - A(H1N1) then some B & A(H3N2)
    • Chile - Lower observed rates than in 2009 - Fewer severe cases. Late Season Rise mostly due to A(H3N2) - A(H1N1) then B & A(H3N2). Early epidemics of RSV
    • New Zealand - Local observed rates higher than in 2009 - Fewer severe cases - Mostly A(H1N1) only
    • South Africa - Lower observed rates than in 2009 - Fewer severe cases - A(H3N2) & B ? no A(H1N1)

    ECDC Comment (11th October 2010):

    As in 2009 the findings from the Southern Hemisphere countries deserve continuing attention. While the global picture was sufficiently like seasonal influenza to allow WHO to declare that the world is in a post pandemic phase that does not mean that everywhere in Europe there will be a benign 2010-2011 season. We do not know what the pattern of the ?new? seasonal influenza will be especially the picture of who the risk groups are (1, 2).

    On the basis of the pandemic, at least one EU country has decided to proactively add pregnant women to their usual recommendations for immunisation (3). The heterogeneous picture in the Southern Hemisphere leaves Europe facing a number of possibilities.

    The late season rises associated with influenza A(H3N2) and B viruses indicates the basis for using trivalent vaccines. Seasonal influenza can anyway show a heterogeneous pattern geographically, however, some of the New Zealand transmission has been sufficiently intense to cause the Ministry concern in that country. The implication could be that parts of European countries that were less affected in 2009 may be more affected in the 2010/2011 season.

    There are serological data which suggest heterogeneous coverage following the early waves in Europe but no analyses as yet following the full 2009/2010 winter (4,5).

    Certainly, these findings emphasise the importance of the autumn immunisation campaigns in Europe as the new trivalent seasonal vaccines become available.

    1. Nicoll A, Sprenger M. The end of the pandemic ? what will be the pattern of influenza in the 2010-11 European winter and beyond? . Euro Surveill. 2010;15(32):pii=19637.

    2. Nokleby H, A Nicoll A Risk groups and other target groups ? preliminary ECDC guidance for developing influenza vaccination recommendations for the season 2010-11. Eurosurveillance March 25th 2010

    3. United Kingdom Department of Health, England The influenza immunisation programme 2010/2011 May 28th 2010

    4. Weekly Epidemiological Record (WER); 11 JUNE 2010, 85th YEAR; No. 24, 2010, 85, 229?236. Seroepidemiological studies of pandemic influenza A(H1N1) 2009 virus.

    5. Miller E, Hoschler K, Hardelid P, Stanford E, Andrews N, Zambon M Incidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study The Lancet, Early Online Publication, 21 January 2010 doi:10.1016/S0140-6736(09)62126-7

    Influenza elsewhere in the world:

    WHO?s most recent global review of influenza was published on 10th October (it is now published every two weeks).

    Apart from the New Zealand and Australian situations already described, WHO reports how varied the pattern of influenza remains in the rest of the world. Mexico has reported an increase in influenza like illness since August, particularly in its south coinciding with an increased proportion of samples testing positive for influenza, mostly influenza A(H3N2). Those epidemics have now subsided.

    Southern India is experiencing epidemics of A(H1N1) 2009 with active transmission in some areas but rates are declining. In contrast in South-East Asia there are reports of increases of activity in Cambodia and Thailand. In Cambodia reports most frequently are of A(H3N2) but there are also H1N1 (2009) detections and a few influenza B viruses.

    Thailand is reporting an increasing number of influenza and local outbreaks of H1N1 (2009).

    The significance of this influenza activity in tropical countries is unclear since in many of the equatorial countries surveillance and testing has improved during and following the 2009 pandemic. Hence normal patterns of influenza activity (the baseline) have yet to be defined. In tropical settings where surveillance is established the pattern of transmission across the months can be quite different from what is seen in the temperate countries.

    WHO also continues to publish its weekly update of virological data including an update on antiviral resistance to August 18th. The former confirms that overall influenza activity has remained at low levels in most parts of the world but that there is co-circulation of pandemic A(H1N1) and seasonal A(H3N2) viruses reported from some countries while influenza type B virus detections have decreased. There are hardly any detections of the previous seasonal A(H1N1) viruses. Almost all the pandemic A(H1N1) viruses are resistant to adamantanes which is also the case with the A(H3N2). There are a few detections of pandemic viruses resistant to oseltamivir from countries with stronger surveillance, all are of the type A(H1N1) H275Y but very few have been shown to represent person to person transmission of resistant virus, i.e. while there have been cases of oseltamivir-resistant pandemic strain infection, these have not achieved the ability to transmit efficiently.