The growing measles outbreak centered in West Texas, with cases reaching into New Mexico and now Oklahoma, is the country’s largest in six years. But experts say that even with more than 250 cases reported across the three states, the outbreak is likely much larger.
“My gut tells me there are cases that are unreported — you don’t have to come in and get tested for measles,” said Katherine Wells, the director of public health in Lubbock, a Texas city on the edge of the outbreak where some sick children have been taken to be hospitalized. “It’s going to be a long process to get everything measles-free again in this area, but I can’t tell you if that’s 500 cases or a thousand.”
Public health officials and other experts believe they are capturing only a fraction of cases for reasons that have to do with the epidemiology of the outbreak as well as reports of a lack of cooperation among some people in the areas where cases have been detected. But a large part of it is simple math.
Texas officials reported last month that an unvaccinated child had died of measles, the country’s first measles death in a decade. In New Mexico, health authorities are investigating another possible measles fatality, an unvaccinated person who tested positive for the virus after death.
The fatality rate for measles is roughly one — perhaps up to three — in every 1,000 cases. Even just the first death put experts on alert that the spread of the virus could be much wider than documented. In 2019, for example, the U.S. reported more than 1,200 confirmed measles cases, largely driven by an outbreak in and around New York City, but no deaths.
“That was the number one flag that this could be greatly underreported,” said Katelyn Jetelina, an epidemiologist who has been tracking the outbreak in her Your Local Epidemiologist newsletter.
In theory, even if the second death is confirmed as having been caused by measles, two deaths in just a couple hundred cases is possible. But statistically, experts would only anticipate two measles deaths to occur in the U.S. with many, many more cases.
“These two individuals could just be incredibly unlucky,” Jetelina said. “It’s just surprising, particularly given how few deaths we’ve had over the past 10 years.”
During measles outbreaks, experts know they’re going to miss cases. But they have an advantage in detecting measles versus other viral infections; measles is accompanied by a telltale rash, meaning parents of sick children are more likely to take them to doctors than they would if they had the flu or Covid. There they would likely get tested. Measles is also a reportable disease, meaning health officials get notified of positive cases.
But in Texas, there have been anecdotal reports that people have resisted efforts to expand testing. In part because of increased frustration with public health since the Covid-19 pandemic, people aren’t as willing to cooperate with case investigations. Some of the same distrust issues that have reduced vaccine uptake in recent years may also contribute to an unwillingness to seek testing.
Experts have noted that some measles patients who have shown up at hospitals have been extremely sick, which suggests that some people are not seeking care unless it becomes an emergency — infections that might have been otherwise documented if people went to a doctor. The person who died in New Mexico never sought medical care at all.
There are also logistical issues. The outbreak is playing out across a very rural stretch of Texas, and while state and local officials have, with federal support, expanded testing access and started another lab in Lubbock to run tests, people might still have to travel extremely far to seek a test. At this point in the outbreak, the publicity around it may have convinced people who are infected but not sick enough to need medical care to just ride out their infection at home.
“I think people know what they’re dealing with because there’s so much information in the news,” Wells said.
That might be especially true among adults who are infected. While the majority of cases in Texas are among kids, 38 adults have been confirmed to have measles. In New Mexico, the cases have mostly been documented in adults. The sizable number of adult cases reflects a shift in the spread of measles, which used to almost always strike in childhood. But now, the kids whose parents avoided vaccination in the 1990s and 2000s have become adults themselves, adding to the pool of people who act as kindling to outbreaks.
In Texas, more than half of the 223 confirmed cases as of Tuesday have been identified in Gaines County, and many have been tied to a Mennonite community there with low vaccine uptake. But cases have also been reported in counties south of Gaines and all the way north to Dallam County, on the Oklahoma border, a stretch of some 300 miles.
On Tuesday, Oklahoma officials also reported two probable measles cases, based on the people’s symptoms and their exposure to cases in the Texas and New Mexico outbreak. State health officials said the two people realized they had been exposed and stayed home through their infectious periods, suggesting they had prevented onward spread.
Health officials say that even if they miss some cases, the more infections they can track, the better they can get their arms around an outbreak. With stronger surveillance, they can know where to surge additional testing and expand outreach with vaccination, the best approach to safely corralling outbreaks.
The outbreak has also taken on a political dimension. During a Tuesday interview with health secretary Robert F. Kennedy, Jr., who has downplayed the severity of the outbreak and also undersold the importance of vaccination to ending it, Fox News’ Sean Hannity referred to the measles outbreak as “relatively small.” Kennedy, reiterating comments he’s made earlier about the outbreak, also noted that there are multiple measles outbreaks every year. (An outbreak is defined only as three or more connected cases, and most only result in a small number of infections.)
Jane Zucker, formerly the assistant commissioner of New York City’s health department, said she started to notice a shift in some people’s willingness to get tested during the 2018-2019 measles outbreak there. Typically during an outbreak, with heightened awareness of the virus, people want to confirm that what they’re sick with is measles. But during the New York outbreak, Zucker said, “a lot of those rules were really broken.”
As she and colleagues wrote in the New England Journal of Medicine, the health department only learned about some infections “several weeks to months” later, when parents would bring kids in for serologic testing — a blood test that can show that someone has immunity to a virus, either from vaccination or a prior infection — so that the kids could get back to school. (Unvaccinated children were only allowed at schools if they could demonstrate they had recovered from an infection.)
As they wrote, “delayed identification of measles in these situations hindered the ability of the Department of Health and Mental Hygiene to implement real-time control measures.”