Global Alert and Response (GAR)

Pandemic (H1N1) 2009 - update 76

Weekly update (more data on virological surveillance)

The Global Influenza Surveillance Network (GISN) continues monitoring the global circulation of influenza viruses, including pandemic, seasonal and other influenza viruses infecting, or with the potential to infect, humans including seasonal influenza.

Since the beginning of the pandemic in 19 April 2009 to 14 November, a total of 82 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 297,366. Of these, 209,614 (70.5%) were pandemic H1N1, 8025 (2.7%) were seasonal A (H1), 23,437 (7.9%) were A (H3), 50,533 (17.0%) were A (not subtyped) and 5757 (1.9%) were influenza B.

For this reporting week (8 November to 14 November 2009); a total of 27 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 16,817. Of these, 15,040 (89.4%) were pandemic H1N1, 130 (0.8%) were seasonal A (H1), 143 (0.9%) were A (H3), 1446 (8.6%) were A (not subtyped), 58 (0.3%) were influenza B.

The above numbers represent only the specimens and results reported to FluNet. Some laboratories (NICs), under pressure of the pandemic surge, do not test for seasonal subtypes and accordingly, this data should be interpreted with caution.

Detailed virological information for the European Region of WHO is included in the EuroFlu Weekly Electronic Bulletin.

From the start of H1N1 pandemic (19 April) till 21st November 2009, cumulatively 150 countries shared a total of 18501 specimens (14477 clinical samples and 4024 virus isolates) with WHO CCs. Armenia, Dominica, Grenada, Madagascar and Switzerland are new countries sharing samples this week. Of these, 13580 specimens (clinical samples and isolates) were tested; 10768 (79.3%) were influenza positive. Of these positives, 6972 (64.7 %) were pandemic H1N1, 2990 (27.8%) were seasonal influenza A, 791 (7.3%) were influenza B.

A virus mutation at position 222 of the amino acid sequence of the haemagglutinin protein of the pandemic virus was recently reported in a few viruses from Norway. The mutation is D222G (aspartic acid to glycine), which, according to a public accessible gene sequence database "GenBank", has also been detected sporadically in viruses from several other countries since April 2009.

This change in the virus has been found in mild as well as severe cases. WHO, through its Global Influenza Surveillance Network (GISN) is monitoring virus mutations that are of potential public health importance.

Systematic surveillance conducted by the Global Influenza Surveillance Network (GISN) including WHO Collaborating Centres (WHOCCs) for reference and research on influenza, continues to detect sporadic incidents of H1N1 pandemic viruses that show resistance to the antiviral oseltamivir. To date, 75 oseltamivir resistant pandemic H1N1 influenza viruses have been detected and characterized worldwide. All of these viruses show the same H275Y mutation. All these viruses remain sensitive to zanamivir. Worldwide, more than 10,000 clinical specimens (samples and isolates) of the pandemic H1N1 virus have been tested and found to be sensitive to oseltamivir.

All pandemic H1N1 2009 influenza viruses analysed to date were antigenically and genetically closely related to the vaccine virus A/California/7/2009.

Virology data update

Download update (.pdf)

For more information