Influenza update - 11 March 2011
Update number 129
Overall, the influenza season of the northern hemisphere appears to be peaking or in decline in most areas, though with continuing active circulation particularly in North America and Eastern Europe. Influenza A(H3N2) comprises the largest proportion of influenza detections in North America. Although influenza A(H1N1)2009 has been the most commonly detected virus in Europe and northern Asia influenza type B has been increasing in Europe and is now the more common virus seen in many countries. The large majority of the viruses characterized are closely related to the vaccine strains included in the current seasonal vaccines. A small number of influenza type B of the Yamagata lineage are reported in North America and Europe, making up about 5 to 7% of B viruses detected.
North America: Influenza activity has remained elevated in much of North America though many indicators are beginning to show a levelling off or decrease in activity. In Canada, increases of influenza activity have been seen in Quebec and British Columbia but is declining in many other regions of the country. The Influenza-like Illness (ILI) consultation rate increased to 36.5 consultations per 1000 patients from 29.3 the previous week but has been relatively stable overall and is within the expected range for this time of year. The proportion of clinical specimens testing positive for influenza (18% in week 8) has continued to decline in recent weeks since peaking in week 52 of 2010. Influenza A(H3N2) remains the most commonly detected virus in Canada accounting for 86% of influenza A viruses for which subtyping was performed. Although influenza A(H1N1)2009 has been increasingly detected in recent weeks, during week 8 H1N1 (2009) decreased to 7% of subtyped viruses. Influenza B detections accounted for the remaining 12% of viruses subtyped. In the United States of America, during week 8, ILI activity remained above baseline nationally but has decreased from previous weeks. Deaths attributed to pneumonia and influenza reported through the 122 Cities Mortality Reporting System remain at the epidemic threshold for the fifth consecutive week. The proportion of specimens testing positive for influenza viruses (28% in week 8) have declined for the second consecutive week. Of the viruses for which subtype information is available, 49% were influenza A (H3N2), 34% were influenza B, and 17% were influenza A(H1N1)2009. In both Canada and the United States, more than 99% of H3N2 and H1N1 (2009) viruses characterized are antigenically similar to the strain contained in the current trivalent seasonal influenza vaccine. Of the influenza B viruses characterized, more than 90% are of the Victoria lineage contained in the current vaccine, with another 5 - 7% from the Yamagata lineage. Influenza activity in Mexico peaked in mid-December 2010 and activity there is currently very low associated primarily with influenza type B.
Europe: Influenza activity is decreasing in the majority of the European countries, more notably in the west. A majority of countries in Europe are reporting decreasing rates of consultation for ILI and Acute Respiratory Infections (ARI). In Western Europe the number of influenza infections with severe outcome also has declined but remained high in Greece. Sentinel surveillance for Severe Acute Respiratory Infections (SARI) indicates declining trends in south-eastern part of the European Region (Kazakhstan, Kyrgyzstan and the Republic of Moldova) while increasing numbers of SARI hospitalizations are reported in Romania, the Russian Federation, and Ukraine. The overall percentage of sentinel specimens testing positive for influenza in the whole of Europe, 36% of 525 specimens collected, is also declining in comparison with previous weeks. Influenza type B now makes up more than half of all influenza viruses detected (51%). Of the influenza A viruses subtyped: 95% were influenza A(H1N1)2009 and 5% were influenza A(H3N2). For severe cases, some differences are noted between the countries of the European Economic Area (EEA) and the rest of the Europe Region. Data from 11 countries of the EEA indicate that H1N1 (2009) is much more commonly detected in severe cases than in outpatients. For eight countries from Central Asia and Eastern Europe, however, the proportions of viruses detected in 206 sentinel SARI specimens were similar to those from ILI cases with 48% testing positive for influenza, 54% of which were influenza A and 46% influenza B. 92% of influenza A viruses tested from SARI cases were H1N1 (2009) and 8% influenza A(H3N2). Similar to North America, nearly all influenza A viruses characterized this season in Europe have been antigenically similar to the H1N1 and H3N2 strains included in the current trivalent seasonal influenza vaccine. Approximately 93% of influenza type B viruses characterized are also of the same lineage as those in the current vaccine (Victoria) with the remainder being of the Yamagata lineage.
North Africa and the Middle East: Influenza activity in North Africa and the Middle East remains low in the countries where data are available. Most countries continue to have limited co-circulation of influenza A(H1N1)2009 and influenza B.
Northern Asia: Overall, influenza activity in the temperate zone of Asia has continued to decrease or remained stable at low level, with the majority of cases involving influenza A(H1N1)2009. Northern China, Japan, Republic of Korea, and Mongolia have all reported declining levels of ILI in recent weeks. In Northern China, influenza activity has remained below the level seen during the previous two seasons, and the proportion of specimens testing positive for influenza has decreased to 13%.
Influenza activity remains low throughout the tropical zone and the most common subtype detected is influenza A(H1N1)2009. Influenza activity is sporadic in regions of Central America, the Caribbean and the Andean Region, with influenza A and B co-circulating. In sub-Saharan Africa, available data indicate little activity in most countries. In Madagascar activity has peaked around week 5 of 2011 and now has a low level of activity with influenza A(H3N2 ) and type B co-circulating. A low level of influenza activity continues in much of tropical Asia, though at declining rates. In Southern China, during 14-20 February, influenza activity has decreased slightly and remains below the level seen last season, and similar to the level seen two seasons ago. During this time period, 28% of the 981 specimens tested were positive for influenza. Of these, 78% were influenza A and 22% influenza B. Of the 274 influenza A detections: 94% were influenza A(H1N1)2009, and 2% were influenza A(H3N2). In Hong Kong Special Administrative Region, influenza activity continues to decrease. Influenza A(H1N1)2009 made up approximately 90% of the 372 viruses subtyped during week 9, with the remaining viruses being influenza A(H3N2) and influenza B.
Most countries in the southern temperate regions of the world continue to have very little influenza transmission since the end of their winter season. Australia continues to detect low, persistent numbers of influenza A(H3N2).
During weeks 7 to 8, regional and widespread outbreaks of laboratory confirmed influenza A(H1N1)2009, A(H3N2) and B viruses continued to be reported in many parts of Asia, Europe and the north Americas while activity deceased in some countries. Influenza A(H1N1)2009 viruses predominated in China, while both A(H1N1) 2009 and B viruses co-circulated in many European countries. In the United States of America, influenza A(H1N1)2009, A(H3N2) and B viruses co-circulated, while in Canada, the predominant viruses were still influenza A(H3N2). The number of laboratory confirmed influenza positive specimens remained low in the southern hemisphere. The vast majority of antigenically characterized viruses from the 2010-2011 influenza season remain similar to the viruses WHO recommended for the 2010-2011 northern hemisphere influenza vaccines.
During weeks 7 to 8 (13 to 26 February 2011), National Influenza Centres (NICs) from 71 countries, areas or territories reported data to FluNet*. A total of 23,736 specimens were reported as positive for influenza viruses, 17,762 (74.8%) were typed as influenza A, 5,974 (25.2%) as influenza B. Of the sub-typed influenza A viruses reported, 80% were influenza A(H1N1)2009 and 20% were influenza A(H3N2).
Influenza virus detection by type/subtype in countries, areas or territories:
- Influenza A(H1N1)2009: Albania, Algeria, Armenia, Australia, Austria, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Cambodia, Canada, China, Croatia, Czech Republic, Denmark, Ecuador, Egypt, Estonia, Finland, France, France - Martinique, Georgia, Germany, Ghana, Greece, Hungary, Iceland, India, Iran (Islamic Republic of), Italy, Japan, Kyrgyzstan, Lao People's Democratic Republic, Latvia, Luxembourg, Mexico, Mongolia, Netherlands, Norway, Pakistan, Poland, Portugal, Republic of Korea, Romania, Russian Federation, Serbia, Singapore, Slovakia, Slovenia, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland, United States of America.
- Influenza A(H1N1) (old seasonal virus): no report.
- Influenza A(H3N2): Albania, Australia, Austria, Brazil, Canada, China, Cuba, Czech Republic, Denmark, France, France - Martinique, Georgia, Germany, Ghana, Italy, Jamaica, Japan, Madagascar, Mexico, Mongolia, Norway, Paraguay, Republic of Korea, Russian Federation, Serbia, Singapore, Spain, Sweden, Turkey, Ukraine, United States of America.
- Influenza A(H5): Cambodia, Egypt.
- Influenza B: Albania, Algeria, Armenia, Austria, Belarus, Belgium, Bulgaria, Cambodia, Canada, China, Costa Rica, Cuba, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Ghana, Greece, Hungary, Iceland, Iran (Islamic Republic of), Italy, Jamaica, Japan, Kyrgyzstan, Lao People's Democratic Republic, Latvia, Lithuania, Luxembourg, Madagascar, Mexico, Netherlands, Norway, Pakistan, Poland, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sri Lanka, Sweden, Switzerland, Thailand, Tunisia, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland, United States of America.
- No influenza activity reported: Afghanistan, Azerbaijan, Bangladesh, Central African Republic, Chile, Colombia, France - French Guiana, France - Guadeloupe, Honduras, Panama, Uruguay.
* Some NICs report to FluNet retrospectively leading to updates of previous summary data.
* Some NICs report to FluNet retrospectively leading to updates of previous summary data.
Source of data
The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.
The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance Network) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.
FluNet data as of 07 March 2011, 14:00 UTC