Scientific opinion on the possible risks posed by the influenza A (H3N2v) virus for animal health and its potential spread and implications for animal and human health

Swine are an important host in influenza virus ecology since they are susceptible to infections with both avian and human influenza A viruses. In 2011 and 2012, clusters of human infection with a swine-origin influenza A(H3N2) variant virus (H3N2v) containing the matrix (M) gene from the 2009 H1N1 pandemic virus were reported in the United States (US). The likelihood of introduction of H3N2v virus into the EU, and subsequent exposure and infection of EU pig herds was assessed. The overall likelihood of a pig holding in the EU being infected by exposure to H3N2v virus through either imported infectious pigs or humans coming from the US was estimated to be low. Efficient separation of imported pigs for 30 days would reduce the likelihood of exposure to a negligible level. The likelihood that H3N2v would spread to other pig holdings was judged to be high, assuming frequent movements of pigs between holdings. Currently, applied real time RT-PCRs can detect all swine influenza A viruses and, combined with gene sequencing, would identify the emergence of H3N2v virus. However, sequencing is not done on a routine basis in EU. Experimental studies in pigs show that the infection is purely of respiratory nature and follows a relatively mild course with fever, coughing and inappetence, similar to that of the endemic swine influenza viruses. Immunity resulting from vaccination with European vaccines may provide some cross-protection against infection with H3N2v virus whereas vaccines based on US swine H3N2 strains would offer superior protection. It is not possible to predict which changes within H3N2v virus might enable it to develop pandemic properties. Hence, it is not possible at present to set up a specific system to monitor such a risk. Nevertheless, it is recommended to reinforce the monitoring of influenza strains circulating in pigs in EU.