Why are measles cases rising in the US? 2026 outbreak hits highest level in decades

Why are measles cases rising in the US? The 2026 outbreak is bringing confirmed infections to their highest annual level in decades, after the disease was declared eliminated more than 20 years ago. The CDC reports more than 2,200 confirmed measles cases nationwide in 2026, already exceeding the total recorded across all of 2025 and marking the largest count since the early 1990s. Cases have been detected in more than 40 states, including New Jersey, Pennsylvania and Washington, D.C. Health officials attribute the resurgence largely to declining MMR vaccination coverage in some communities, creating pockets of susceptibility. The CDC and Johns Hopkins tracking data indicate most cases involve people who were unvaccinated or whose vaccination status was unknown. Officials warn sustained transmission could put US elimination status at risk.