We collected patient-specific data as described previously [3] , although vaccination status against H1N1 2009 virus was collected only during 2010. We divided patients into the age groups used in a previous report [9] . We calculated the duration of ICU and hospital stay and ICU occupancy rates for Australia and New Zealand. We recorded patient outcomes at ICU and hospital discharge status or as still in hospital or in ICU as of 15 October 2010 for patients admitted in 2010 and as of 23 November 2009 for patients admitted in 2009. Finally, we obtained data on vaccination in both countries.