The measles vaccine has in several community studies from different parts of the world been shown to have a non-specific beneficial effect on child mortality. That means that the protection against death mediated by the vaccine exceeds the disease specific effect, ie the vaccine not only prevents deaths caused by measles, but also other deaths, presumably due to a non-specific immune stimulation providing protection from other infections than measles. For example, during the war in Guinea-Bissau that broke out on June 7, 1998, the population fled and the health care system broke down. There was no routine vaccination for at least a 3 months period. Hence, when the war started there was a group of infants who had been randomised to early SW measles vaccination at 6 months or IPV and who did not receive the standard-titre SW measles vaccine at 9 month that they would otherwise have been given. This natural experiment represents the first randomised study of the mortality effect of SW measles vaccine. The mortality ratios for measles vaccinated children were 0.29 (0.08-1.03, p=0.041) and 0.31 (0.10-0.94) over the first 3 and 7 months of the war.