Measles elimination: Old and new challenges?

Life attenuated measles vaccines have dramatically reduced measles morbidity and mortality world-wide. Despite high vaccination coverage, measles outbreaks continue to occur both in developed and developing countries. While secondary vaccine failure may be responsible for disease in some seroconverted individuals, evidence suggests that many more vaccinees who are protected against disease may not be fully protected against virus infection. In low-income developing countries protection by maternal antibodies seems to erode faster than previously estimated especially in infants who were born to vaccinated mothers. Problems of infectivity and susceptibility of vaccinees will be compounded in case wild-type viruses become less sensitive to vaccine induced immunity. These observations suggest that elimination may be more easily achieved as long as large proportions of populations are protected by wild-type virus-induced immunity.