Health and Human Services Secretary (HHS) Robert F. Kennedy Jr. came under fire from former U.S. Surgeon General Dr. Jerome Adams for encouraging vaccine skepticism amid a measles outbreak that is currently raging along the Texas-New Mexico border.

The nation’s former top medical official, stated in a CNN op-ed on Thursday that the vaccine’s drop in the Mennonite community in Texas, where the outbreak started, demonstrates how quickly measles can spread in an unprotected population.

The current measles outbreak, which has spread to three states, is a clear reminder of how important herd immunity is to protecting our communities. The outbreak started in Gaines County, Texas, and has already spread to 321 recorded cases, 38 hospitalizations, and two fatalities, including an unvaccinated school-age child.