The biological consequences of the H275Y mutation in the NA gene of pH1N1 influenza virus, which confers resistance to oseltamivir, are important because the drug is a first-line treatment for patients who present with pandemic influenza infection. Drug resistance was already observed in infected individuals in the community and in the clinic during the first and second waves of the swine flu pandemic 4,13 although it did not spread widely. Whether oseltamivir-resistant pH1N1 viruses might disseminate in subsequent waves through the community is key to future public health planning.