ECDC risk assessment: 2009 influenza A(H1N1) pandemic (Update 20 May 2009)

Risk assessment

A new influenza A(H1N1) virus was first identified by US CDC on 17 April 2009 in samples from two Californian children. It was reported in MMWR on 21 April [1]. The basic genetic structure of the virus which was first described in Eurosurveillance on 30 April [2], demonstrated that the virus had many genetic elements from porcine (swine) influenza. The new virus was thus initially called ‘swine flu’ even though its pig origin later came into question, and it is now clearly evident that it can spread from human to human.