What is the primary cause of measles outbreaks in the U.S.?

The primary cause of measles outbreaks in the U.S. is primarily linked to unvaccinated individuals bringing the virus from other countries. Measles is a highly contagious viral infection, and if a person who is not vaccinated travels to an area where measles is more prevalent, they can contract the virus and then introduce it to the U.S. population.

While the measles vaccine, part of the MMR (measles, mumps, and rubella) vaccine, is highly effective in providing immunity, and vaccination coverage in the U.S. is generally high, clusters of unvaccinated individuals can lead to outbreaks when these unvaccinated individuals come into contact with someone who has traveled from an area with a measles outbreak. The presence of unvaccinated individuals is a critical factor because it diminishes herd immunity, which is essential for preventing the spread of contagious diseases like measles.

Ultimately, increased awareness and action around vaccination, particularly in the context of travel, are vital to preventing measles outbreaks associated with imported cases.