The Atlantic For years, the worst outcomes of measles were all but unknown in America. Now they look inevitable. Of every 1,000 people the measles virus infects, it may kill as few as one to three. In a way, this can seem merciful. But the mathematics of measles is also unforgiving. The virus is estimated to infect roughly 90 percent of the unimmunized people it encounters; each infected person may pass the infection on to as many as 12 to 18 others. In large part owing to an ongoing outbreak in South Carolina, the United States is watching those risks unfold in real time. As of last Thursday, the CDC is reporting 982 cases of measles. That count is expected to break 1,000 this week; a tracker run by researchers at Johns Hopkins University that many experts consider more reliable has ticked past 1,000 already. By the numbers alone, another death seems inevitable, and inevitable soon.
Probabilities aren’t guarantees, of course. So far, 2026 may be seeing some improvements over 2025, when the U.S. documented more than 2,200 measles cases—more than in any year since 1991. This year, just 4 percent of measles cases have led to hospitalization, compared with 11 percent last year. Several factors could be contributing to that discrepancy, including how hospitals in South Carolina are reporting measles admissions or of more mild cases being diagnosed to begin with; experts aren’t yet sure.
That 4 percent, however, still represents 40 or so people who have ended up in the hospital with at least one of the conditions that can make measles so devastating—among them, pneumonia, respiratory failure, and brain disease. In South Carolina, multiple people, including children, have been hospitalized with a form of brain swelling called encephalitis, which can lead to permanent intellectual disability or deafness, and in some cases turn fatal.