Vaccination changing age of disease onset
The age at which people are susceptible to certain viruses and bacteria is changing with the mass vaccination programs. For example, mass vaccination with Hib (haemophilus influenza type B) shifted the disease from infants and small children to adults. The measles vaccine shifted the disease from normal at risk groups to very small babies and adults, who are more likely to suffer serious complications or death. Vaccine Safety Manual by Neil Z. Miller. (Preface)
From 1966 to 1968, before the rubella vaccine was licensed, just 23 percent of all cases occurred in persons 15 years of age or older. By 1975, just a few years after the rubella vaccine was introduced, 62 percent of all rubella cases were in the 15-or-older group. In 1976 and 1977, this figure rose to more than 70 percent. By 1990, 81 percent of all rubella cases occurred in this older age group. From 1994 to 1997, 85 percent of all rubella cases were in persons 15 years of age or older. Source: CDC MMWRs. Government figures show that cases of congenital rubella syndrome (CRS) increased after the rubella vaccine was introduced. Source: CDC, MMWR (October 25, 1996). Vaccine Safety Manual by Neil Z. Miller. p178