Like every single live-action Disney movie out this year, measles is making the comeback no one asked for. Already, there have been more than 700 cases of the viral and vaccine-preventable disease reported in the U.S. this year—a record high since it was eradicated in the country nearly 20 years ago.
Things could get much worse, though. And according to new research published Thursday, there are certain U.S. counties where measles could still hit hard this year.
Measles is no longer found naturally in the U.S., thanks largely to a mandatory vaccination program that has made it impossible for the disease to maintain a constant foothold here (like smallpox and polio, humans are the only hosts for the virus). But people can contract measles elsewhere and then bring it back to the U.S. Ordinarily, even these cases shouldn’t cause a major outbreak, because most people, in most places, are vaccinated against measles. In areas where the vaccination rate dips below a certain level, though, the highly contagious disease can do what it does best and spread like wildfire.
So the Johns Hopkins researchers behind this study, published in the journal Lancet Infectious Diseases, created a predictive model to spot the top 25 counties where the risk of a sustained outbreak would be highest in 2019.
“We actually started working on this in February. And it’s funny, because we’ve had to constantly update it. So this whole time, we’ve basically been seeing the outbreak evolve as the patterns we predicted are happening,” study co-author Lauren Gardner, an associate professor of civil engineering at Johns Hopkins, told Gizmodo by phone.
The model doesn’t just factor in a county’s vaccination rate (excluding people with medical exemptions) as past attempts to quantify measles risk have, but also where recent and current outbreaks elsewhere in the world have happened and their size, as well as the amount of international travelers from these countries that these counties typically receive.
“Basically, a measles outbreak only happens if there are two things in play. There has to be a group of unvaccinated individuals, and there has to be the introduction into that area,” Gardner explained. “So the hotspots are hotspots for one of two reasons, or some combination of them. It’s either they have communities with low vaccination rates, or they have a lot of inflow from other countries that are having big outbreaks.”
Included in the list are counties in Washington, New York, and Oregon that have already been part of major measles outbreaks, such as Multnomah, Oregon. It also includes areas that are right next to counties with outbreaks, such as Queens, New York. Queens and the adjacent Brooklyn have together reported more than 450 cases of measles as of early May, mostly among pockets of unvaccinated residents in the Orthodox Jewish community. And of the 45 counties that have reported measles cases as of mid-April, 30 are either included in the team’s list or are adjacent to them.
Here’s the full list of counties that the researchers found to be at most risk for a measles outbreak in 2019, in order of likelihood (note that some have already experienced or are currently experiencing outbreaks):
Cook, Illinois; Los Angeles, California; Miami-Dade, Florida; Queens, New York; King, Washington; Maricopa, Arizona; Broward, Florida; Clark, Nevada; Harris, Texas; Honolulu, Hawaii; Wayne, Michigan; Tarrant, Texas; Multnomah, Oregon; Orange, Florida; Essex, New Jersey; Denver, Colorado; Hillsborough, Florida; San Mateo, California; Salt Lake, Utah; Suffolk, Massachusetts; Clayton, Georgia; Travis, Texas; Hennepin, Minnesota; Loudoun, Virginia; San Diego, California.
While public health officials are already hard at work trying to stop current outbreaks, Gardner and her co-authors say their findings should be used to help guide prevention efforts in the near future. So far, 23 states have reported measles cases this year, including Arizona, Colorado, Florida, Texas, and Illinois. Some counties in these states could still be at risk for further outbreaks, according to their model, as could states that haven’t experienced one yet, such as Hawaii, Minnesota, Utah, and Virginia.
“We would definitely say these places need to be targeted for vaccination campaigns, so that any gaps are addressed,” Gardner said. At the same time, she added, there should also be broad disease surveillance efforts of people traveling from countries identified as high-risk measles hotspots, which include India, China, Mexico, Japan, Ukraine, Philippines, and Thailand, according to their research.
Of course, this study is the latest reminder that in an ideal world, most people shouldn’t have to be worrying about measles and other vaccine-preventable diseases at all.
“These are really preventable outbreaks, and there’s no reason we should be seeing measles outbreaks in the U.S. today,” Gardner said. “I think the big issue is that people underestimate the risk of not getting vaccinated, and they overestimate the risk of vaccination.”