Measles cases in the U.S. are rising as major health organizations call for higher vaccination rates and experts fear the virus will proliferate among unvaccinated populations.
Most notably, this year’s number of measles cases now exceeds last year’s total.
As of Thursday, there were 64 confirmed cases in 17 states, compared to 58 cases for all of last year. according to to the US Centers for Disease Control and Prevention (CDC). The count is in Chicago on Friday grew by two to a total of 17.
“Measles is one of the most contagious diseases known to man,” said Dr. David Nguyen, an infectious disease specialist at Rush University Medical Center.
Experts say these incidents could be similar to the outbreak that stretched across 31 states in 2019, when 1,274 patients fell ill and 128 were hospitalized in the worst measles outbreak in the US in decades.
Yet the measles, mumps and rubella (MMR) vaccine is extremely effective. Just one dose provides around 93% protection against infections, while the second dose is 97% effective – and the protection is often lifelong. Treatments, isolation and airborne precautions also stop the spread of the virus.
“Any measles outbreak is completely preventable,” said Dr. Aniruddha Hazra, an associate professor of medicine at the University of Chicago.
The American Medical Association has a appeal to increase vaccination rates, while the CDC has a health advice urging providers to ensure that all travelers, especially children over six months of age, receive the MMR vaccine. Normally the first dose of the vaccine is given at one year of age, meaning babies are particularly at risk from outbreaks. But after six months of age, an additional dose can be given if a baby may be exposed to active cases.
Most cases — 93% last Monday — were linked to international travel and most cases involved children old enough to be vaccinated, the CDC says. Measles represents a major global threat, with more than 9 million cases 136,200 deaths against measles, especially children, by 2022.
There were last month 10 cases of measles in South Florida, most of which are linked to an outbreak at an elementary school, and doctors are still searching for cases because of the virus’s long incubation period.
Florida Surgeon General Dr. Joseph Ladapo controversially went against the CDC’s recommendations Allowed unvaccinated children exposed to measles to return to school without quarantine. It’s not clear whether Florida officials held vaccination campaigns to boost immunity in schools. Local school officials declined to comment on the matter.
In Chicago, one case of measles was reported earlier this month before the virus arrived at a shelter for migrants, many of whom previously did not have access to health care such as vaccines.
“Measles was already prevalent in Chicago, but like any other communicable disease, it often migrates to vulnerable communities,” says Hazra. “The perfect storm is happening.”
About 1,900 people live close together in a former warehouse. In Chicago more than 11,000 people are currently staying in shelters like this one, which were hastily converted to house the nearly 37,000 migrants who have arrived in the city since 2022. These individuals were sent on buses and planes on orders from Texas Governor Greg Abbott.
The Chicago Health Department quickly administered nearly 1,000 MMR vaccines at the affected shelter, and “people are lining up to get this vaccine,” Hazra said. The CDC has also deployed a team to assist with contact tracing and isolation procedures.
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Hazra noted that “measles has a very long incubation period,” meaning that “contact tracing and isolation” with this disease “can be deployed more successfully than we were able to do with Covid-19.”
Ninety percent of unvaccinated people become infected if exposed to measles. The virus can remain in the air for hours and infect people never come into direct contact with a patient. Each patient can infect an average of 1 12 to 18 other people if the community is not protected by vaccines.
Typically, at least one in five unvaccinated measles patients require hospitalization, and nearly a fifth of children develop pneumonia. One in six hundred babies not yet eligible for vaccines suffer a fatal neurological complication, and about one in a thousand children develop encephalitis, or swelling of the brain, which can lead to convulsions, deafness and intellectual disabilities.
Measles can also be the cause immune amnesiamaking people more vulnerable to other infections in the months and years after a case.
“In 2000, we declared measles eliminated in the U.S.,” Nguyen said. With sparks of cases threatening to erupt into sustained outbreaks among unvaccinated communities, that status could become “threatened,” he said.
“We need a lot of people vaccinated and immune in the population to stop its spread,” Nguyen said. “If you are not vaccinated, you should get vaccinated.”
In 2021, 91.6% of children over two years of age had received at least one MMR vaccine. But the proportion of preschoolers protected by vaccines fell from 95.2% in the 2019-2020 school year to 93.1% in 2022-2023.
In outbreaks like 2019, the virus can find a niche of unvaccinated people in a community and spread like wildfire.
“These numbers will continue to rise year after year as we see an erosion of vaccine confidence,” Hazra said. “And it won’t just be measles, but other vaccine-preventable diseases that we have nearly eradicated in this country in recent decades.”