When Texas officials first discovered measles cases this year, they were among the Mennonite population. Now, officials say cases are spreading to other communities.

Texas' outbreak, which has largely spread in undervaccinated Mennonite communities, could last a year, based on studies.

The measles vaccine uses a weakened virus that's never been shown to spread to others. Samples from the outbreak in Texas also show that a wild-type virus is responsible. Yet, social media posts have falsely claimed that the outbreak is due to a vaccine strain.