The presence of IgG-anti-p-H1N1-09 antibodies in all the severe Indian patients (HI antibodies in all the 4 screened) does indicate switch from the innate to adaptive immunity. Poor outcome despite the switch may probably be attributed to the timing of the shift or role of antibodies in disease severity. Significantly higher titres of IgG-anti-p-H1N1-09 antibodies in the critically ill patients supports the role in pathogenesis. This observation is in sharp contrast with that for the SARS patients examined from Canada [13] documenting significantly lower anti-SARS CoV spike antibody titres in the critically ill patients. Though the presence of neutralizing antibodies protect against Influenza virus infection, clearance of the infection is mediated by cellular immunity. The exclusive presence of IgG1 antibodies in both patient categories document Th2 bias with significant enhancement with severity. This observation correlates with the elevated levels of TLR3, 4, and 7, Th2 cytokines (IL6 and IL10) at protein level and IL4, IL5, IL6, IL10 at gene level.