Simultaneous control of measles and rubella by multidose vaccination schedules.

There is currently a preference for using measles-mumps-rubella vaccine to simultaneously control these three diseases. Here an age-specific transmission model is used to investigate the consequences, on cases of measles and congenital rubella syndrome, of switching from a one-dose vaccination with this vaccine to a two-dose vaccination schedule. The model allows for a period of maternally acquired immunity and assumes that infection leads to permanent immunity, while vaccine-induced immunity is allowed to wane. The vaccination coverage at the second dose is expressed in terms of availability for vaccination, which depends on whether the individual received the first dose and the age of the individual. It is found that the optimal age for the first vaccination is not very sensitive to variations in the force of infection and is close to age 1 year for both measles and rubella. However, the optimal age for a second vaccination, offered indiscriminately, depends significantly on the age-specific forces of infection. This emphasizes that decisions about immunization schedules require reliable information about age-specific forces of infection in the community. In some circumstances control may be significantly more effective when the ages for the second dose differ for measles and rubella. It is found that the addition of a catch-up vaccination, offered to previously unvaccinated children at school entry, makes it more feasible to find a common age for the second dose that controls both measles and rubella effectively.