During the initial phase of the pandemic, designated wards in the government hospitals admitted every mild case, treated with Oseltamivir and discharged after recovery. A special intensive care unit treated the critically ill patients. The present study was undertaken during this very early phase of the pandemic. To understand the basis of differential disease presentation/outcome, we investigated 26 mild cases and 15 critically ill patients during 1 st August -19 th September 2009. This report provides comparative data on viral load, cytokines, gene-profiling, Toll-like-receptor (TLR) levels, antibody titres and antibody isotypes.