After public health experts declared measles elimination in the US in 2000, the US Centers for Disease Control and Prevention (CDC) established seven indicators of measles elimination status to ensure that the country remained on track. Now, analyzing these same indicators, researchers at Boston Children’s Hospital have found that the US missed four of the seven criteria, while others are at risk. These findings have been published The Lancet.
Researchers conducting the analysis included Maimuna Majumdar, PhD, MPH, the inaugural Peter Szolovits Distinguished Scholar in the Computational Health Informatics Program at Boston Children’s, and her postdoctoral research fellow Anne Bishop, MD, a pediatrician and German National Academy of Sciences Leopoldina Fellow. The team evaluated the number of US measles cases, the outbreak, their origin, and the level of transmission. Their results show that measles is making a comeback in the US, spreading steadily for more than a year.
The latest series of US outbreaks began in Texas in January 2025. Since then, the outbreak has spread to 45 states. When the US was last recertified for measles elimination status in 2011, the country had achieved all measles elimination indicators established by CDC’s National Immunization Program. But this year, according to this new research, most indicators are in the red.
Missing indicators of measles elimination status:
- Low number of cases with a cutoff of less than one case per 10 million people. By early 2026, there were about 93 cases per 10 million people in the US, exceeding this limit.
- Most cases of measles must come from abroad rather than from internal spread. Since the beginning of 2025, only 6-7 percent of measles cases have come from abroad, meaning the majority of cases have come from within the US.
- Limited number of outbreaks (cutoff of about four) and no more than about six cases each. Last year, 48 outbreaks in the US resulted in more than 2,000 cases. And by early 2026, at least 19 outbreaks resulted in more than 1,600 cases.
- Transmission rate less than one, meaning an infected person spreads measles to fewer people than one other person on average. The US has exceeded this rate more than 75 percent of the time since the beginning of 2025.
Indicators at risk:
- The country has achieved the four-week target in terms of all infections coming from outside the US. Since the first infection in January 2025, not even four weeks have passed without infection in the US and 90% of the cases have been found here.
- herd immunity through vaccination. An estimated 95 percent of people need to receive two-doses of measles vaccine, usually given as part of the MMR (measles, mumps and rubella) vaccine, to achieve herd immunity. However, the US average vaccination rate for kindergartners in the 2024-2025 school year was 92 percent, meaning this indicator is at high risk. For example, vaccination rates in Texas are 79 to 90 percent low, according to the team’s earlier study.
- There is no common viral strain in measles cases. From ongoing genetic analyses, preliminary data suggest that the majority of cases involve the same viral strain and are likely part of the same transmission chain.
“The decline in vaccination rates is already a warning sign that measles could be back,” Bishops said. “However, losing position would be a clear and very worrying indicator.”
Researchers believe these findings make a strong case for vaccinating children from an early age.
“Viral infections are not all benign and measles infection can cause lifelong problems even after recovery,” Majumdar said. “Children under the age of one year are among those at highest risk for serious complications, and the full effects on children exposed during the current outbreak may only appear years later.”
The data are intended to provide insight/early warning framework ahead of the Pan American Health Organization expert panel meeting in November 2026 to reassess the measles elimination status of the Americas.
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