Specifies the type of date that is specified in an immunization forecast. The immunization forecast defines the schedule for a vaccine based on variables like the subject's age, the type of vaccine, and the supply unit. The immunization forecast may involve multiple administrations in a series or just one administration. Each of the administrations has one or more recommended dates. Examples: * Earliest recommended date * Recommended date * Latest acceptable date * Overdue date (date after which to start sending reminders)