caused by Haemophilus influenzae (Hib), a major cause of bacterial meningitis and other serious diseases in children, have decreased by over 99% in the US since the introduction of a vaccine in 1988. It is estimated that full vaccination, from birth to adolescence, of all US children born in a given year would save 33,000 lives and prevent 14 million infections. There is anti-vaccine literature that argues that reductions in infectious disease result from improved sanitation and hygiene (rather than vaccination) or that these diseases were already in decline before the introduction of specific vaccines. These claims are not supported by scientific data; the incidence of vaccine-preventable diseases tended to fluctuate over time until the introduction of specific vaccines, at which point the incidence dropped to near zero. A Centers for Disease Control and Prevention website aimed at countering common misconceptions about vaccines argued, "Are we expected to believe that better sanitation caused the incidence of each disease to drop, just at the time a vaccine for that disease was introduced?" Another rallying cry of the anti-vaccine movement is to call for randomized clinical trials in which an experimental group of children are vaccinated while a control group are unvaccinated. Such a study would never be approved because it would require deliberately denying children standard medical care, rendering the study unethical. Studies have been done that compare vaccinated to unvaccinated people, but the studies are typically not randomized. Moreover, literature already exists that demonstrates the safety of vaccines using other experimental methods. Other critics argue that the immunity granted by vaccines is only temporary and requires boosters, whereas those who survive the disease become permanently immune. As discussed below, the philosophies of some alternative medicine practitioners are incompatible with the idea that vaccines are effective. Population health Incomplete vaccine coverage increases the risk of disease for the entire population, including those who have been vaccinated, because it reduces herd immunity. For example, the measles vaccine is given to children 9–12 months old, and the window between the disappearance of maternal antibody and seroconversion means that vaccinated children are frequently still vulnerable. Strong herd immunity reduces this vulnerability. Increasing herd immunity during an outbreak or when there is a risk of an outbreak is perhaps the most widely accepted justification for mass vaccination. When a new vaccine is introduced, mass vaccination can help increase coverage rapidly. If enough of a population