As measles cases in West Texas are still on the rise two months after the outbreak began, local public health officials say they expect the virus to keep spreading for at least several more months and that the official case number is likely an undercount.

Vaccination efforts have faltered, and many residents have turned to alternative treatments endorsed by Robert F. Kennedy Jr., the health secretary.

Measles outbreaks in West Texas and New Mexico now have 351 cases in total. Two unvaccinated people have died from measles-related causes. The U.S.