[Breakthrough measles - risk factors and clinical manifestations; low transmission rate and less complications than in primary measles].

Despite the existence of a highly effective vaccine, measles may appear in some vaccinated individuals after exposure to wild type measles virus. Reduced circulation of the measles virus in the population in low-endemic countries results in an absence of viral challenge and may cause waning of immunity over time after vaccination. Another reason for breakthrough infection is primary vaccine failure due to immunological conditions or defective measles virus vaccine. Exposition to a high dose of measles virus without proper protective respiratory masks may increase the risk of breakthrough measles, as has been reported in some outbreaks where health care workers were exposed. The clinical symptoms in breakthrough measles are often milder than in primary measles. Respiratory symptoms and conjunctivitis are less common than in primary measles. The contagiousness of breakthrough measles is low and in some cases negligible.