The world has been declared to be in a post pandemic phase by WHO that is according to the WHO criteria “Levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance.“ However careful attention has to continue to be paid to what is happening with seasonal influenza as what will be seen now is a new seasonal influenza pattern perhaps different in its detail from before the pandemic. 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. This is being done using epidemic intelligence techniques consulting routine and non-routine published sources in five temperate Southern Hemisphere countries with developed long-term epidemiological and virological surveillance systems: Argentina, Australia, Chile, New Zealand and South Africa.
The special interest this year is because these are the first countries to experience the 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.
As normal, seasonal influenza transmission started to rise after May or June in 2010 in these Southern Hemisphere temperate countries (see Figures below). Low but rising levels of seasonal influenza (H3N2 and type B) viruses but without influenza A(H1N1) were detected from June 2010 onwards in South Africa. 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 are none of the previous seasonal A(H1N1) viruses. It should be noted that Chile also routinely detects and reports on respiratory syncytial virus (RSV) and this drove early epidemics of respiratory infection in children (see figures for Chile). Overall four of the countries: Argentina, Australia, Chile and South Africa have experienced levels of transmission in the community and hospitalisation quantitatively less than that the last 2009 Southern Hemisphere winter when there were pandemic waves. Though Australia and Chile are now experiencing late seasonal rises. All four countries are also reporting few cases of severe disease associated with influenza and generally neither health services nor 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. Argentina and South Africa have already ceased publishing weekly reports on their respective MoH websites. This bi-weekly update therefore focuses on new information from Chile, Australia and New Zealand (see graphs below).
Chile: In the latest influenza report from Chile (reporting from 29th August - 4th September 2010) it is noted that an increase in respiratory consultations has been observed during the previous 5 weeks. Conversely RSV circulation, which was responsible for local epidemics in children, have decreased during the last weeks (36% of the total of viruses), followed by influenza B and parainfluenza viruses. In addition, the co-circulation of 2009 pandemic influenza A(H1N1) and H3N2 viruses continues with the latter becoming more important, the proportion of the A(H3N2) viruses being three-fold higher than the proportion of the 2009 pandemic influenza A(H1N1) virus.
Australia: In the reporting period 21-27th August 2010 (week 34), data from a number of surveillance systems indicate that influenza activity is now rising late in the season and and that while overall national rates of ILI consultations in primary care remain well below levels observed during the 2009 winter pandemic wave, there is now widespread ILI activity in South Australia and Victoria and regional activity in the rest of mainland, except in the capital county where transmission is classified as local. The proportion of sentinel respiratory samples testing positive for influenza virus has not changed in the last two weeks, remaining at around 14% but that is a figure considerably higher than earlier in the season. The majority (70%) 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. There are no data indicating to what extent the transmission has been affected by attempts at immunisation in 2009 and 2010 with first pandemic and then seasonal influenza vaccines in Australia.
New Zealand: In this country the weekly surveillance report for week 35 records that the reported national rate for influenza-like illness (ILI) during the last two weeks has peaked and it is already decreasing steadily towards the national baseline level, being at present already lower than it was in the 2008 season, and lower than it was at this same time last year during the 2009 pandemic (see New Zealand figure below). To date the Ministry of Health Reports there have been 18 deaths linked to influenza though the risk factors for these deaths are yet to be reported. Thirteen of these deaths have so far been confirmed as being due to A(H1N1). As of September 9th there have been 669 hospitalisations of laboratory-confirmed cases of pandemic influenza H1N1, including 9 people with confirmed H1N1 currently in intensive care. So far this year, a total of 104 people with confirmed H1N1 have been admitted to intensive care (these figures do not include influenza-like illness among people admitted to hospital without a positive H1N1 laboratory test result). 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. It has suggested by the authorities that areas that experienced less transmission during the pandemic winter wave of 2009 may now be experiencing more transmission. There is some support for this in the seroprevalence data that were reported by the New Zealand authorities at the end of last winter where seroprevalence rates by locality varied from 20% to 30% (1). However overall rates of ILI and numbers of severe and fatal cases in New Zealand remain below levels seen during the winter 2009 pandemic wave and the current seasonal epidemics shows evidence that they have passed its peak. Equally through there are some localities in New Zealand where levels of reported influenza like illness are above those seen in 2009 pandemic winter. In Australia there is some heterogeneity in the clinical reports from state by state reports but it is only in New Zealand that this heterogeneity has driven the all age incidence rate of ILI to such high levels. There are no data indicating to what extent the local transmission has been affected by intensive attempts at immunisation with first pandemic and then seasonal influenza in New Zealand.
ECDC Comment (13th September 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 (2,3). It is interesting that, on the basis of the pandemic, at least one EU country has decided to proactively add pregnant women to their usual recommendations for immunisation (4). The finding of heterogeneous transmission in New Zealand and perhaps also Australia will need careful watching and interpretation. Of course seasonal influenza can 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 (5,6). Certainly, these findings emphasise the importance of the autumn immunisation campaigns when the new trivalent seasonal vaccines become available.
1. Bandaranayake D, Huang S Seroprevalence of the 2009 influenza A (H1N1) pandemic in New Zealand ESR May 2010
2. 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.
3. 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
4. United Kingdom Department of Health, England The influenza immunisation programme 2010/2011 May 28th 2010
5. Weekly Epidemiological Record (WER); 11 JUNE 2010, 85th YEAR; No. 24, 2010, 85, 229–236. Seroepidemiological studies of pandemic influenza A(H1N1) 2009 virus.
6. 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: For this, ECDC draws attention to WHO’s latest review of influenza in the world published on 10 September (now published every two weeks). It is commended for its many links. Apart from the New Zealand and Australian situations already described, WHO also reports that the situation in India as causing local concern though not worsening. Transmission of influenza H1N1 (2009) virus transmission is still locally intense in certain parts of the country most notably in the states of Kerala and Maharashtra but also in several other western and southern states (Gujarat, Andhra Pradesh, Karnataka, and Tamil Nadu). Between mid-June 2010 and the second week of August 2010, the state of Maharashtra reported consecutive weekly increases in the number of new cases, including numbers of new fatal cases; the epidemic does not appear to have yet peaked in Maharashtra but the rate of increase in the numbers of new cases appears to have slowed. The epidemic appears to have stabilized or begun to decline in some other affected states. Seasonal influenza B viruses are also known to be currently circulating in India, although at lower levels than H1N1 (2009) viruses. The significance of this influenza activity in tropical countries like India 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. For example in Hong Kong and Southern China peaks in the early Spring and June-August are usually reported while in India it is suggested that influenza transmission usually intensifies when the monsoon starts as happened in July in parts of India.
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.
Figures for acute respiratory infections needing emergency care in children (niños) and adults (adultos) from Chilean Ministry of Health (Ministerio de Salud de Chile) for week 35
Unusually among the five countries Chile reports on the isolation of a number of viruses and this can be seen in the diagram below which shows the importance of respiratory syncytial virus (VRS) in both 2009 and 2010 and this is thought to partially explain the surge in referrals for acute respiratory infections in children (ninos) seen above.
Figure confirmations of viruses in Chile in 2009 and 2010
Influenza Surveillance Report No. 34 for the week 21 to 27 August 2010
Figures from New Zealand Influenza Weekly Update 2010/35