Under Díaz, the population grew steadily from 11 million in 1877 to 15 million in 1910. Because of very high infant mortality (22% of new babies died) the life expectancy at birth was only 25.0 years in 1900. Few immigrants arrived. Diaz gave enormous power and prestige to the Superior Health Council, which developed a consistent and assertive strategy using up-to-date international scientific standards. It took control of disease certification; required prompt reporting of disease; and launched campaigns against tropical disease such as yellow fever.