Global Alert and Response (GAR)

Pandemic (H1N1) 2009 - update 75

Weekly update (Virological surveillance data)

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 7 November, a total of 81 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses by NIC laboratories was 272,326. Of these, 187,290 (68.8%) were pandemic H1N1, 7771 (2.9%) were seasonal A (H1), 23,019 (8.5%) were A (H3), 48,653 (17.9%) were A (not subtyped) and 5593 (2.1%) were influenza B.

For this reporting week (1 November to 7 November 2009); a total of 30 countries reported to FluNet. The total number of specimens reportedly positive for influenza viruses was 10,954* (update for last week: 15,634). Of these, 8660 (79.1%) were pandemic H1N1, 28 (0.3%) were seasonal A (H1), 14 (0.1%) were A (H3), 2199 (20.1%) were A (not subtyped), 53 (0.5%) 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 14th November 2009, cumulatively 145 countries shared a total of 17720 specimens (13771 clinical samples and 3949 virus isolates) with WHO CCs. Of these, 13309 specimens (clinical samples and isolates) were tested; 10521 (79.1%) were influenza positive. Of these positives, 6764 (64.3 %) were pandemic H1N1, 2963(28.2%) were seasonal influenza A, 779 (7.4%) were influenza B.

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, 57 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.

* Data might be incomplete due to a lag for reporting from some countries. Graphs associated with this update are set up till week 44, since some countries have delayed reporting to FluNet

Virology data update

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