Pneumonia and UVB during the 1918-19 pandemic infleunza in the U.S. William B. Grant, Sunlight, Nutrition, and Health Research Center (SUNARC) 18 January 2010 Sir: Additional support for this finding is given in an ecological study of case-fatality rates following infection by pandemic influenza A/H1N1 in 12 U.S. communities in 1918-19. Using data obtained by the U.S. Public Health Service through door-to-door surveys near the end of the 1918-19 pandemic , along with indices for solar ultraviolet-B (UVB) doses in summer and winter, it was determined that differences in vitamin D production in summer explained 46% of the variance, while vitamin D production in winter explained 42% of the variance . The mechanisms proposed were shifting of cytokine production away from proinflammatory ones by 1,25-dihyroxyvitamin D and combating pneumonia infection by cathelicidin induced by 1,25-dihydroxyvitamin D. References 1. Britten RH. The incidence of epidemic influenza, 1918–19. Pub Health Rep 1932;47:303-39. 2. Grant WB, Giovannucci D. The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918–1919 influenza pandemic in the United States. Dermato-Endocrinology 2009;1(4): 215-9. http://www.landesbioscience.com/journals/dermatoendocrinology/article/9063/ Competing interests I receive funding from the UV Foundation (McLean, VA), the Vitamin D Society (Canada), the Sunlight Research Forum (Veldhoven), and Bio-Tech-Pharmacal (Fayetteville, AR).