Much of the journalism concerning H1N1 influenza virus continues the simplistic infectious disease model that it is a virulent virus which can be managed with handwashing and vaccination.1 The infectious disease model suggests that lower standards of living and medical care explain these disparities. A more plausible explanation is available. The response to H1N1 may be one of two types: severe inflammatory response syndrome (SIRS) versus mild influenza. It has been known for years that distinct populations behave differently after organ transplantation. One of the mechanisms proposed for this difference is the type of immune response mustered. Is the development of SIRS with H1N1 a Th2 phenomenon and could it explain the susceptibility of pregnant women and Aboriginal or Mexican populations to this complication? The cytokines produced in the Th2 response have been implicated the development of SIRS.2 The type of immune response a person has on contact with H1N1 determines the outcome and it may be that a Th2 or similar response heralds severe complications. It is to be hoped that a reduction in incidence of H1N1 influenza with vaccination will compensate for any change in the rate of H1N1-related SIRS. Science would have been preferable to hoping-for-the best but it is too late for that now. Footnotes For the full letter, go to: www.cmaj.ca/cgi/eletters/181/6-7/E102#191579 REFERENCES 1. Hebert PC, MacDonald N. Preparing for pandemic (H1N1) 2009. CMAJ. 2009;181:6–7. 2. Miller AC, Rashid RM, Elamin EM. The “T” in trauma: the helper T-cell response and the role of immunomodulation in trauma and burn patients. J Trauma. 2007;63:1407–17. [PubMed]