Measles cases in the US are rising, as major health organizations plead for increased vaccination rates and experts fear the virus will multiply among unvaccinated populations.
Most notably, this year’s tally of measles cases has now outpaced last year’s total.
On Thursday, there were 64 confirmed cases in 17 states, compared with 58 cases in the entirety of last year, according to the US Centers for Disease Control and Prevention (CDC). By Friday, the tally in Chicago 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 that these incidents could approach the outbreak that spanned 31 states in 2019, when 1,274 patients got sick and 128 were hospitalized in the worst US measles outbreak in decades.
Yet the measles, mumps and rubella (MMR) vaccine is extremely effective. Just one dose offers about 93% protection against infection, 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.
“Every measles outbreak can be entirely preventable,” said Dr Aniruddha Hazra, associate professor of medicine at the University of Chicago.
The American Medical Association has issued an appeal to increase vaccination rates, while the CDC released a health advisory urging providers to ensure all travelers, especially children over six months, receive the MMR vaccine. Typically, the first dose of the vaccine is given at one year of age, which means babies are at particular risk in outbreaks. But an extra dose may be given after six months of age if a baby may be exposed to active cases.
Most of the cases – 93% by last Monday – had been linked to international travel and most cases have been among children old enough to be vaccinated, the CDC says. Measles represents a major global threat, with more than 9m cases and about 136,200 deaths from measles, primarily children, in 2022.
Last month, there were 10 measles cases in south Florida, most of them linked to an outbreak at an elementary school, and doctors are still on the lookout for cases due to the long incubation period of the virus.
The Florida surgeon general, Dr Joseph Ladapo, controversially went against CDC recommendations and allowed unvaccinated children who had been exposed to measles to return to school without quarantining. It’s not clear if Florida officials held vaccination campaigns to bolster immunity in schools. Local school officials declined to comment on this issue.
In Chicago, one measles case was reported earlier this month before the virus landed at a shelter for migrants, many of whom did not have access previously to healthcare like vaccines.
“Measles was already here in Chicago, but like any communicable disease, they often migrate to vulnerable communities,” said Hazra. “The perfect storm is occurring.”
About 1,900 people live in close quarters in a former warehouse. In Chicago, more than 11,000 people currently reside in shelters like these, 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 by order of Greg Abbott, the Texas governor.
Chicago’s 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 also deployed a team to help with contact tracing and isolation procedures.
Hazra noted that “measles has a very long incubation period”, meaning “contact tracing and isolation can be leveraged” more “successfully with this disease than we were able to do with Covid-19”.
Ninety per cent of unvaccinated people will become infected if they are exposed to measles. The virus can linger in the air for hours and infect people who never come into direct contact with a patient. Each patient can infect an average of 12 to 18 other people if the community is not protected by vaccines.
Typically, at least one in five unvaccinated measles patients need to be hospitalized, and nearly one-fifth of children develop pneumonia. One in 600 babies who are not yet eligible for vaccines suffer from a fatal neurological complication, and about one in 1,000 children develop encephalitis, or brain swelling, which can lead to convulsions, deafness and intellectual disabilities.
Measles can also cause immune amnesia, making people more vulnerable to other infections in the months and years following a case.
“In 2000, we declared measles eliminated in the US,” Nguyen said. As the sparks of cases threaten to erupt into sustained outbreaks among unvaccinated communities, that status may be “under threat”, he said.
“We need a lot of people to be vaccinated and immune in the population for it to stop spreading,” Nguyen said. “If you’re not vaccinated, you should get vaccinated.”
As of 2021, 91.6% of children over the age of two had received at least one MMR vaccine. But the share of kindergarteners protected by vaccines fell from 95.2% in the 2019-20 school year to 93.1% in 2022-23.
In outbreaks like the one seen in 2019, the virus can find a niche of unvaccinated people in a community and spread like wildfire.
“These numbers will continue to rise, year to year, as we see erosion in vaccine confidence,” said Hazra. “And it’s not just going to stop at measles, but also other vaccine-preventable illnesses that we have been close to eradicating in this country for the past decades.”
