Influenza is a contagious respiratory illness caused by influenza viruses. It is characterized by a sudden onset of fever, headache, myalgia, malaise, prostration, non-productive cough, sore throat, and rhinitis. It has usually a short incubation period, from 1 to 3 days. Most people recover within one to two weeks without any medical treatment. However, severe illness and death during annual influenza epidemics occur primarily among the very young, the elderly and those debilitated by chronic diseases such as cardiac diseases, pulmonary diseases, renal diseases or diabetes, cancer, and immunocompromised conditions. In addition, when a novel strain of influenza appears, it can cause a pandemic. Since the vast majority of the human population has no immunity to such a novel strain, there would be high morbidity and mortality during the pandemic.
The influenza vaccine is considered to be the most effective preventive measure. Therefore, WHO recommends vaccination of high-risk groups including the elderly, people with weakened immune systems and those with underlying chronic diseases to reduce the disease burden from influenza. WHO also urges increased vaccination coverage in health care workers who have frequent contact with these vulnerable populations.
Situation Updates
31 January 2012
Data up to week ending in 21 January 2012 (latest data variable by country)
In the Northern Hemisphere countries, ILI activity increased and influenza season has arrived in some countries. The influenza activity in northern China, however, was stable during the week 9-15 Jan. The percentage of ILI visits in national sentinel hospitals was 3.7%, which was slightly lower than the previous week (3.8%) and lower than the same period of the previous year (4.4%). Among 736 ILI specimens, 120 (16.3%) samples were positive for influenza: 7 were influenza A (5 A/H3N2, 2 subtypes not determined) and 113 were influenza B (110 lineages not determined, 3 B/Victoria). During the week 9-15 Jan, ILI activity increased in Japan. The number of ILI cases per sentinel reporting site was 7.33, which was higher than the previous week. Of the 1093 influenza viruses detected since 5 Sep 2011, 984 (90.0%) were A/H3, 5 (0.4%) were A/H1N1pdm and 101 (9.2%) were influenza B; so far in Jan, 474 were A/H3, 1 was A/H1N1pdm and 27 were influenza B. In the Republic of Korea, during 15-21 Jan, ILI activity also increased. The number of ILI cases per 1 000 outpatient was 18.8, which was higher than the previous week. So far for the 2011-2012 influenza season, 922 samples tested positive for influenza (837 A/H3N2 and 85 influenza B). In Mongolia, during 9-15 Jan, ILI activity increased although the majority of samples continued to be non-influenza.
In the subtropics/tropics, ILI activity also increased. In southern China, however, ILI activity was stable. During the week 9-15 Jan, the percentage of visits that were ILI in sentinel hospitals was 3.4%, which was lower than the previous week (3.7%) but slightly higher than the same period of the previous year (3.0%). 486 of 1146 (42.4%) specimens were positive for influenza: 455 (93.6%) were influenza B (454 lineage not determined, 1 B/Victoria) and 31 (6.4%) were influenza A (22 A/H3N2, 1 A/H1N1pdm and 8 subtypes not determined). In Viet Nam, during 8-15 Jan, 1 of 23 ILI samples (4.3%) was positive for influenza (1 A/H3). In Cambodia, among 87 ILI samples, 3 specimens tested positive for influenza (all influenza B) during 1-7 Jan. In Lao PDR, among 39 ILI samples tested during 8-15 Jan, 4 (10.2%) tested positive for influenza (all influenza B). In Hong Kong (China), during 15-21 Jan, the overall ILI activity continued to increase; of the 196 samples positive for influenza during this week, 140 (71.4%) were influenza B, 52 (26.5%) were influenza A/H3, 1 (0.5%) was influenza A (untyped), and 3 (1.5%) were influenza A/H1N1pdm. In Singapore, acute respiratory infection (ARI*) activity was stable during 15-21 January. The proportion of cases with ILI among the polyclinic ARI cases was low at 1%. Of 171 ILI samples collected in the last four weeks, 55% (preliminary) were positive for influenza virus. Of all influenza isolates collected in Jan 2012, influenza B constituted 67%, whilst influenza A /H3N2 and influenza A/H1N1pdm constituted 22% and 10%, respectively.
In the Southern Hemisphere, ILI activity continued to remain low. During 8-15 January in Australia, 121 ILI samples were received and 20 (16.5%) tested positive for influenza (12 A/H3 and 8 influenza B).
In the Pacific Islands, for the week ending 22 January, ILI activity has been variable. No Pacific Country or Territory reported weekly case numbers above the threshold of 90% of its historical value.
*ARI defined as clinical diagnosis of acute upper respiratory tract infection (ICD9 460 – 465: Acute Nosopharyngitis (common cold); 461 Acute Sinusitis; 462 Acute Pharyngitis; 463 Acute Tonsillitis; 464 Acute Laryngitis and Tracheitis; 465 Acute Upper Respiratory Infections of Multiple or Unspecified Sites; 466 Acute Bronchitis and Bronchiolitis). ILI defined as temperature >38C with cough
or sore throat.
Past Situation Updates
Fact sheets
News and press releases
22 June 2009
Deaths and two new countries in the Region affected
[full text]
05 March 2008
The Philippines checks its ability to avert a flu pandemic
[full text]
06 July 2005
International conference draws up strategy to fight avian influenza
[full text]
30 June 2005
WHO Stresses the Threat from Avian Influenza Has Not Receded
[full text]
24 June 2005
International Team of Avian Influenza Experts Visits Viet Nam
[full text]
[more news]
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