Weekly influenza surveillance overview, 30 January-5 February 2012 - Week 5

• Medium influenza activity was reported by 11 countries and increasing trends by 18 countries.• Among 1 444 sentinel specimens, the percentage positive for influenza was 42% with a range of 3–85% across countries.• Of 600 sentinel specimens that tested positive for influenza virus, 95.7% were type A and 4.3% were type B. Of the 782 sentinel and non sentinel influenza A viruses sub-typed, 97.7% were A(H3) and 2.3 % were A(H1)pdm09.• Since the start of the season, 394 SARI cases have been reported from six countries. Of the cases with confirmed influenza, 80% were associated with A(H3), 13% with A(H1)pdm09 and 7% with B viruses.• To date, no resistance to neuraminidase inhibitors (oseltamivir and zanamivir) has been reported this season.• Influenza activity continued to increase in week 5, though with significant variation across Europe and no clear geographic progression. The dominant virus remains A(H3N2).