The WHO strongly recommends administration of antiviral treatment as soon as possible to all hospitalized patients during the post-pandemic influenza season [34]. In the present study, however, time from illness onset to receipt of antiviral therapy was significantly longer in patients hospitalized in the post-pandemic period than during the pandemic. Importantly, a large proportion of patients did not receive antiviral therapy on the day of arrival at the hospital, in spite of previous results from observational studies of hospitalized patients with pandemic (H1N1) 2009 showing that early antiviral treatment was associated with a decrease in viral load, disease severity and mortality [35–39]. Therefore, it can be hypothesized that the delay in the administration of antiviral treatment during the first post-pandemic influenza season may explain at least in part the differences in severity and outcomes found between the study periods. It is important that physicians should be aware that patients presenting with pneumonia in the emergency department during the upcoming influenza seasons may have influenza A (H1N1) 2009 and may require a targeted diagnostic and therapeutic approach.