RT Journal Article SR Electronic T1 Winter mortality modifies the heat-mortality association the following summer JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP 245 OP 251 DO 10.1183/09031936.00037808 VO 33 IS 2 A1 Rocklöv, J. A1 Forsberg, B. A1 Meister, K. YR 2009 UL http://erj.ersjournals.com/content/33/2/245.abstract AB The present study aimed to investigate how the heat-related increase in deaths in summer and the extent of mortality displacement depend on influenza and other categories of mortality in the previous winter, which when low leaves a greater pool of susceptible individuals. Mortality data from Stockholm, Sweden, from 1990–2002 were stratified into a summer period and a winter period. A Poisson regression model was established for the daily mortality in the summer, with temperature and confounders as explanatory variables. In addition, indicators of total, respiratory, cardiovascular and influenza mortality of the winter period were incorporated as effect modifiers in the summer model, and lagged effects in strata defined by indicators were studied. A high rate of respiratory as well as cardiovascular mortality in winter reduced the heat effect the following summer, and influenza mortality tended to do so as well. The cumulative effect per °C increase was 0.95% below and 0.89% above a threshold (21.3°C) after a winter with low cardiovascular and respiratory mortality, but -0.23% below and 0.21% above the threshold after a winter with high cardiovascular and respiratory mortality. The current study shows that high respiratory, cardiovascular and influenza mortality in winter leads to lower temperature effects in the following summer. It also suggests that persons for whom influenza may be fatal are often also susceptible to heat and this subgroup might, therefore, not benefit as much as expected from influenza vaccinations.