US measles cases have reached 297 in the first five months of 2026, the highest incidence since 2019, driven by vaccination coverage falling below the 95 percent threshold needed for herd immunity in multiple communities. The outbreaks are concentrated in areas where organized vaccine refusal has reduced local immunization rates to 75 to 80 percent, sufficient to sustain transmission.
Public health officials emphasize that measles is among the most contagious human infections, capable of infecting nearly 90 percent of unvaccinated individuals exposed in the same indoor space. The MMR vaccine is 97 percent effective after two doses and has an exceptional safety record across billions of doses administered. The current outbreaks are occurring predominantly in communities where misinformation has created unfounded fears about vaccine safety.
