In summary, the need for a second dose of rubella vaccine is unproven. The rare cases of rubella occurring in the United States are in unvaccinated persons, without signs of spread to the general population, suggest that a second dose of rubella vaccine may not be needed. Although titers decrease with time, high rates of seropositivity are maintained. Indeed, considering the long incubation period of rubella (14–21 days) an anamnestic response in vaccinees following exposure may offer sufficient protection, making the presence of detectable antibodies at the time of exposure unnecessary.