Measles is a highly contagious viral disease that spreads through respiratory droplets, such as from coughing or sneezing. Before the measles vaccine became available in 1963, measles caused widespread epidemics globally, affecting millions and leading to significant mortality each year. Despite its historical impact and high contagiousness, once a person has been infected with measles, they generally develop lifelong immunity and cannot contract the disease again.
Robust Immunity After Measles Infection
Natural measles infection triggers a robust immune response that leads to enduring protection. When the virus enters the body, the immune system identifies it and initiates a specific defense, involving the generation of specialized immune cells like B and T lymphocytes. B lymphocytes produce specific antibodies to neutralize the virus, while T lymphocytes eliminate infected cells. After the initial infection clears, many of these specialized B and T cells persist in the body as memory cells. These memory cells allow the immune system to recognize the measles virus rapidly upon future exposure, mounting an effective response and preventing a second illness.
Understanding Apparent Second Cases
While natural infection provides robust, lifelong immunity, some individuals may believe they have experienced measles more than once. True reinfection with the measles virus is exceedingly rare. Instead, such apparent “second cases” are almost always due to a misdiagnosis. For example, the initial illness might have been another rash-causing viral infection like rubella (German measles) or roseola, which share some symptoms with measles. The “second” illness could also be a misdiagnosis of a different viral infection, or in rare instances, laboratory errors or reporting inaccuracies could contribute to the perception of reinfection.
Natural Immunity Versus Vaccine Protection
Immunity acquired from natural measles infection provides lifelong protection for most individuals. Similarly, the measles-mumps-rubella (MMR) vaccine also offers highly effective and long-lasting protection against measles. The MMR vaccine works by introducing an attenuated, or weakened, form of the measles virus, which stimulates the immune system to produce antibodies and memory cells without causing the full-blown disease. Two doses of the MMR vaccine are recommended and are about 97% effective at preventing measles. Both natural infection and vaccination are highly effective methods for preventing subsequent measles disease.