Australia has reported oseltamivir resistance of A(H1N1)2009 influenza virus in the state of New South Wales, with assumed person-to-person transmission of the resistant strain. The European Centre of Disease Prevention and Control (ECDC) has produced a rapid risk assessment to assess the situation.
The oseltamivir-resistant cases had no known link to oseltamivir exposure and were not immunosuppressed, but were closely linked geographically. Samples from the cluster do not currently exhibit any resistance to zanamivir. Although the cluster has remained localised, it cannot be assumed that the variant virus will not spread. However such viruses were observed transmitting in Europe at low levels last season. In Europe, specifically in the UK, during the 2010–2011 influenza season, routine surveillance found some resistant cases, with no known exposure to oseltamivir in community settings.
ECDC concludes that at present, the risk of this cluster becoming more widespread and having public health implications remains low. However, if spread does occur, there will be implications for the prophylaxis and treatment of influenza patients and the consequences for public health in Europe will need to be considered.
Regardless of the outcome, constant antiviral resistance monitoring is vital in Europe and globally. Only ongoing surveillance will indicate whether this occurrence remains a localised event or whether it has the potential to become widespread.
Oseltamivir and zanamivir are active ingredients in antiviral drugs (Tamilfu, Relenza). Vaccination, supplemented by personal hygiene measures, remains the primary measure for prevention of seasonal influenza transmission. However, antiviral drugs are important countermeasures for prophylaxis and treatment, especially in vulnerable people and those with severe influenza.
Read the full ECDC risk assessment: Oseltamivir-resistant influenza A(H1N1)2009 cluster in Australia
Influenza risk assessments