Weekly influenza surveillance overview, 30 December 2011 - Week 51

• During week 51/2011, low influenza activity was notified by all 21 countries reporting.• Of 539 sentinel specimens collected during week 51/2011 and tested, 35 (6.5%) were positive for influenza viruses. Although this is still a low percentage, it has increased over the last four weeks. • Of 271 influenza A viruses from sentinel and non-sentinel sources sub-typed since week 40/2011, 248 (91.5%) were of the H3 subtype.• Since week 40/2011, 105 severe acute respiratory infection (SARI) cases have been reported by five countries. Twenty-three of them were confirmed influenza cases and of those typed or subtyped nine were due to A(H1N1)pdm09, three were A(H3) and two were influenza B viruses.• With little evidence of sustained transmission in EU/EEA countries at week 51, the annual influenza seasonal epidemic in Europe is yet to start.