Influenza update - 26 August 2011
Update number 141
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- From the peer-reviewed literature
- Virological surveillance
• Influenza activity in the temperate regions of the northern hemisphere remains low or undetectable.
• Countries in the tropical zone mostly reported low influenza activity with the exception of a few countries of the Americas (Dominican Republic, Cuba, Honduras and Brazil), Western Africa (Ghana, Cameroon and Senegal), and Southern Asia (India, Bangladesh, Thailand, and Singapore) that report continued transmission.
• In South America the reported influenza season has been very mild so far with variation in the predominant type and subtype of virus circulating in different countries of the area. Influenza activity in South Africa is continuing at low levels, though the season has peaked. In Australia, influenza-like illness (ILI) consultations and laboratory-confirmed influenza cases continue to increase with a mix of influenza A(H1N1) 2009 and influenza B, which are unevenly distributed across the country. ILI activity in New Zealand remains around expected levels and the majority of viruses detected have been influenza B.
The countries in the northern hemisphere temperate zone are in their inter-seasonal period for influenza. Nearly all of the countries in this zone reported low or no influenza activity.
In Central and tropical South America, a few countries reported low levels of influenza transmission. In the Dominican Republic, influenza transmission continued but with an increasing proportion of influenza type B among the influenza viruses detected, in contrast with previous weeks where influenza A(H1N1)2009 was predominant. The number of samples testing positive in Cuba for influenza increased in comparison with previous weeks, with influenza A(H3N2) counting for the large majority. In Honduras, the proportion of hospitalizations for Severe Acute Respiratory Infection (SARI) increased and is higher compared with 2010 but not in a range considered alarming; influenza A(H3N2) is the most common influenza virus detected. Other Central American countries reported no or very low influenza activity. In tropical South America, Colombia, which has had active circulation of influenza A(H1N1)2009 over the last 10 weeks has reported no new influenza cases. Transmission in Brazil peaked about 8 weeks ago and is now at low levels with small numbers of influenza B, influenza A(H1N1)2009 and influenza A(H3N2). Transmission in Peru and Bolivia has also returned to low levels.
In sub-Saharan Africa, influenza transmission has continued in the west. Ghana is reporting ongoing but decreasing transmission of influenza B together with smaller numbers of influenza A(H3N2) and A(H1N1)2009. Transmission in Cameroon is increasing with higher numbers of specimens testing positive for influenza in recent weeks, predominantly influenza B and much smaller numbers of influenza A(H1N1)2009. Senegal, has reported small numbers of influenza A(H3N2) viruses over the past several weeks which appear to have peaked in mid July. In eastern Africa, Kenya reported continued transmission of a mixture of influenza B, A(H3N2), and A(H1N1)2009 since the peak of transmission in March.
Influenza activity in most of tropical Asia remained low with some notable local areas of transmission. Bangladesh, India, and Thailand continue to report moderate influenza transmission, predominantly influenza A(H3N2) with smaller numbers of both influenza A(H1N1)2009 and influenza type B. Viet Nam continues to report sustained transmission of influenza A(H1N1)2009, which has been continuous since the first of the year. In Cambodia low level detection of influenza A(H1N1)2009 and influenza type B was reported. In Singapore, the proportion of acute respiratory cases with ILI presenting to the polyclinics was low in July at 2%, but 44% (preliminary) of specimens tested positive for influenza virus, predominantly influenza A(H3N2).
Low level influenza activity was reported in the temperate regions of South America. Several indicators of influenza activity indicate that the season has been mild compared to previous years up to this point, though the season is not yet over. In Chile, ILI activity, admissions for respiratory infections in children, and number of samples testing positive for influenza remain low. Two deaths associated with influenza A(H1N1)2009, which accounts for more than 95% of the detected influenza viruses, were registered over the last 2 reporting weeks. The situation in Argentina is similar with low and decreasing levels of ILI and SARI activity and fewer samples testing positive for influenza. In Paraguay, the proportion of ILI consultations was similar to the previous week (~8%) and the proportion of SARI hospitalizations and the proportion of SARI intensive care unit (ICU) admissions remained below 5% and 15% respectively; the proportion of SARI cases that died has declined to less than 5% after an increase for three consecutive weeks reaching 11%. The percentage of specimens testing positive for respiratory viruses remained under 10% with few influenza A(H3N2) detections. In Uruguay, the proportions of SARI hospitalizations and SARI ICU admissions decreased below 5% and 15% respectively. The percentage specimen from SARI cases testing positive for influenza had increased progressively between epidemiological week 25 to week 30 from 1% to 36%. Notably, the distribution of influenza virus types and subtypes has not been consistent across the region. While Chile has reported a large majority of influenza A(H1N1)2009 viruses throughout this season, nearly all of the influenza viruses reported by Argentina in recent weeks have been either influenza A(H3N2) or unsubtyped. Paraguay and Uruguay have had predominantly influenza A(H3N2) and A(H1N1)2009 respectively.
Influenza transmission in South Africa has continued at low levels since peaking in early June. The influenza season there has been predominantly influenza A(H1N1)2009, with much smaller numbers of influenza type B and some influenza A(H3N2).
Australia, New Zealand and South Pacific
The influenza season is still ongoing in Australia and New Zealand. ILI consultations have continued to rise nationally in Australia with the highest number of laboratory confirmed notifications of influenza reported in Queensland, New South Wales and South Australia. The weekly number of laboratory confirmed influenza notifications being reported nationally is above the peak levels experienced in previous years, except 2009. Other surveillance systems also reflect active transmission with ILI activity reported by the Australian Sentinel Practices Research Network continuing to increase and Emergency Department presentations for respiratory disease in Western Australia at above baseline levels. Fifty five percent of ILI presentations to New South Wales (NSW) Emergency departments were between 15 and 34 years. Total admissions to critical care units in NSW have remained within the usual range for the time of year. The Influenza Complications Alert Network Sentinel Hospital System in Victoria, South Australia, Western Australia and the Australia Capitol Territory has reported 51 hospitalizations including 5 ICU admissions associated with influenza since 1 May 2011. Over half of the hospitalizations and 80% of ICU admissions have been associated with influenza A(H1N1)2009 infection. The mean age of patients hospitalized has been 47.3 years. The Australian Paediatric Surveillance Unit reported 21 hospitalizations associated with sever influenza complications in children from 1 July till 9 August, including 8 ICU admissions with the majority associated with influenza A(H1N1)2009; one third of severe cases had chronic underlying conditions. In 2011, 10 influenza associated deaths have been notified nationally so far with a median age of 53.5 years. Eight of the cases were reported as having an influenza A(H1N1)2009, one with influenza type B and one with an un-subtyped influenza A infection. In NSW, the death registration data up to 22 July 2011 was below the seasonal threshold for this period with 1. 6 pneumonia or influenza associated deaths per 100 000 population.
The previously high proportion of influenza B in South Australia has started to decline with increasing numbers of influenza A(H1N1)2009 notifications. The majority of states and territories have reported mostly influenza A(H1N1)2009 with co-circulation of influenza B, except in Tasmania where it is mostly influenza B and Western Australia were there is mostly influenza A(H1N1)2009 circulating.
In New Zealand, the rate of national ILI consultations was 48.5 per 100 000 (185 ILI consultations) and remains around baseline level after rising slightly above the baseline for a few weeks. Influenza type B virus accounts for the majority of influenza viruses detected in New Zealand.
The United States Advisory Committee on Immunization Practices (ACIP) recommendations on the use of seasonal influenza vaccines for the 2011-12 season were released this week, recommending universal influenza vaccination for all persons six months of age and older; optimally given before the onset of influenza activity in the community. The 2011-12 seasonal vaccine virus strains for the Northern Hemisphere are identical to those in the 2010-11 vaccine; however, based on a review of available evidence that indicate that post vaccination antibody titers decline over the course of a year, annual vaccination for all persons is being recommended in the United States to ensure optimal protection even when the strains remain identical to the previous season vaccine. The report further details the available evidence on immunity in children between 6 months and 8 years of age and finds that there is sufficient evidence of the impact of immunity "priming" to recommend that if children did not receive a dose of seasonal influenza vaccine in the 2010-11 season, they should receive two doses of the 2011-12 vaccine at least 4 weeks apart, and that children who were vaccinated in 2010-11 should receive one dose of the 2011-12 vaccine. The report also contains guidance on vaccination of persons reporting allergies to eggs, and describes the available vaccine presentations together with their target age groups, and information as to the mercury and ovalbumin (egg protein) content.
Comment: The ACIP recommendations to revaccinate this year even though the composition of the influenza vaccine has not changed is consistent with the WHO policy of annual vaccination of high risk individuals. Both policies reflect the observation that influenza antibody levels induced by influenza vaccination decrease over time and may leave vaccinated individuals susceptible to infection. In addition, persons at very high risk of influenza complications such as the very old, those with chronic debilitating illnesses, and persons with immunodeficiency may not respond initially to vaccination and cannot be presumed to have immunity because of previous vaccination.
(References: Grohskopf, L., et. al. Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. MMWR Recomm Rep. 2011 Aug 18; 60. in press.; WHO, Meeting of the Strategic Advisory Group of Experts on immunization, April 2011 – conclusions and recommendations. Weekly Epidemiological Record 2011 May 20; 86:21: 205–220.)
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.