A sudden decline in U.S. childhood MMR vaccination rates has left millions of children at increased risk for measles, mumps, and rubella, a new Johns Hopkins-led study released today in JAMA reveals. With over 1,000 cases of measles and at least three reported deaths this year—numbers not seen in decades public health officials fear the country is careening toward losing its hard-won herd immunity, reactivating once-eradicated illness in communities where vaccine coverage has collapsed in the post-pandemic period.The nationwide average kindergartener MMR vaccination rate has fallen from 93.9% prior to the pandemic to 91.2% in 2024—a decline of 2.7 percentage points. This might seem marginal, but it puts the nation perilously short of the 95% level required for herd immunity—the point at which community immunity can stop widespread measles outbreaks.This is the first large-scale analysis to compare county-level vaccination coverage across so broad a representation of the U.S. population. The researchers analyzed data from 2,066 counties in 38 states and specifically targeted children aged five—by which age both doses of the MMR vaccine should have been given.The new publicly released dataset—developed by the same team that created the world-renowned Johns Hopkins COVID-19 dashboard—is also giving a detailed snapshot of vaccination levels. The data is crucial to pinpointing counties that are at high risk for outbreaks in the future, particularly as measles cases also start increasing across the country.Just four states- California, Connecticut, Maine, and New York, experienced MMR increases. The others saw decreases, with Wisconsin recording some of the lowest county-level rates of coverage.Measles had been eliminated in the U.S. in 2000. Flash-forward 25 years, and the landscape has completely changed. In the first half of 2025 alone, more than 1,000 measles cases were confirmed in 31 jurisdictions and states, with three deaths—the first measles deaths in a decade. The CDC says that 97% of those infected had not had even one dose of the MMR vaccine.The ongoing outbreak is localized in Texas but extends to large metropolitan and rural counties equally, reaching states like California, Florida, Illinois, and Pennsylvania. The experts are cautioning that the situation will become endemic if the vaccination levels keep declining.The decline in MMR vaccine uptake coincides with the explosive rise of anti-vaccine misinformation, much of which is promoted by social media sites. A study conducted by Columbia University revealed that disinformation is propagated online more quickly than evidence-based interventions can combat it.Robert F. Kennedy Jr., currently U.S. Health and Human Services Secretary, has long been involved with the anti-vaccination movement. Even in public office, Kennedy has made public claims about the uselessness of the MMR vaccine and held out pseudoscientific alternatives such as Vitamin A or "natural immunity," assertions refuted by the broader scientific community.Fueling the flames, Texas lawmakers just signed into law a bill that will make it easier for parents to get kids into school without current MMR or other child immunizations. Exemption requests in Texas alone have increased more than doubled since 2018—from 45,900 to over 93,000 in 2024.Understanding Herd Immunity and Measles TransmissionMeasles is frequently quoted as the most infectious virus that has been known to humans. It is estimated by the CDC that 90% of exposed non-immune persons will be infected. Even more worrisome, the virus can remain airborne for two hours after an infected individual leaves a room, thus public places such as schools and clinics are extremely susceptible.The MMR vaccine has a success rate of 97% when given two doses, the first at 12-15 months and the second at 4-6 years old. Exposure to other countries or to the community may require early vaccination in infants as young as six months.95% or better vaccine rate guarantees that outbreaks are not viable, safeguarding those individuals who are at risk and cannot be vaccinated because of medical issues or age. With 91.2%, the U.S. is now perilously short of that mark.Is US Repeating 2019 or 1990?The U.S. is currently seeing the most cases of measles in one year since 2019, when there were 1,274. Before that, 1990 stands as the worst year ever, with more than 27,000 cases. The trend is unmistakable—whenever vaccination levels decline, measles comes back with a vengeance and speed.This year's epidemic, omitting 2019, is the largest in more than 30 years. Disturbingly, the majority of cases are occurring among unvaccinated children, so the disease is not only preventable but simply unnecessary.Professor Gardner emphasizes the urgency, "This isn't just about data—it's about our collective health. Every percentage point we lose puts thousands of children at risk."While this research is based in the U.S., its implications are worldwide. Vaccine reluctance, partisan politics, and misinformation are not issues exclusive to America. Countries all over Europe, Asia, and Africa are observing similar declines in routine vaccination after COVID. The U.S. data provides a key guide to prevention, readiness, and policy change globally.