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Despite its elimination in the US in 2000, measles cases are being reported across the country. As of February 22, 35 cases have been reported this year in Arizona, California, Florida, Georgia, Indiana, Louisiana, Maryland, Minnesota, Missouri, New Jersey, New York City, Ohio, Pennsylvania, Virginia, and Washington, according to the US Centers for Disease Control and Prevention (CDC). The CDC cautioned in a January alert that between December 1, 2023, and January 23, 2024, the agency was informed of 23 confirmed cases, most among children and adolescents who were eligible for vaccination but had not received the vaccine. Seven of those cases were imported by international travelers—travel-related cases present a danger to people who are unvaccinated and undervaccinated.
Tina Tan, MD, president-elect of the Infectious Diseases Society of America, said it’s important to understand how quickly measles can spread. “We live in a very mobile world where I don’t think people realize that an infectious disease can travel from one side of the world to the other in less than 24 hours,” she said in an interview with JAMA. According to the CDC, clinicians should especially watch for measles symptoms among patients who traveled abroad to countries with ongoing outbreaks. As of early February, Yemen, Azerbaijan, Kazakhstan, India, Ethiopia, and Russia had the world’s highest case numbers.
Understanding the Cases
Clinicians at the Children’s Hospital of Philadelphia (CHOP) diagnosed the state’s first confirmed measles case this past December—an infant too young to be vaccinated who had traveled outside the US. During the hospital stay, 3 individuals without measles immunity were exposed and later tested positive for measles, according to Lori Handy, MD, MSCE, the associate director of the Vaccine Education Center at CHOP, where she is also an attending physician in the Division of Infectious Diseases. CHOP “recommended home isolation for 21 days, which didn’t happen,” Paul Offit, MD, director of the Vaccine Education Center and professor of pediatrics in the Division of Infectious Diseases at CHOP, said in an interview with JAMA. At least 7 more cases followed in Philadelphia, he noted. When clinicians diagnosed the initial patient at CHOP, “most young physicians had never seen measles, so they didn’t really know what to look for,” Offit said. To help them, “we described what a morbilliform rash looks like and explained the 3 C’s: cough, congestion, and conjunctivitis.” Before the first measles vaccine became available in the US in 1963, most children contracted the disease by age 15 years.
Annually, about 48 000 people were hospitalized, and between 400 and 500 died. Measles resurged about 2 decades after it was eliminated as an endemic disease from the US, with more than 1200 confirmed cases across 31 states in 2019. And in late 2022, more than 70 cases were reported in Ohio alone.The uptick in outbreaks isn’t exclusive to the US. A joint report from the CDC and the World Health Organization published this past November estimated that compared with 2021, 2022 saw an 18% increase in measles cases and a 43% increase in measles-related deaths worldwide. “Even one case of measles is worrisome because it’s highly, highly contagious,” Offit said. Direct contact isn’t necessary for measles to spread. The CDC notes that about 9 out of 10 unprotected people exposed to measles become infected; 1 in 5 cases in which the patient isn’t vaccinated results in hospitalization.
Vaccination Strategies
The CDC recommends that patients 12 months or older be vaccinated against measles; those traveling abroad can be vaccinated as early as 6 months. A single dose of the measles-mumps-rubella vaccine is approximately 93% effective at preventing measles; 2 doses boost protection to about 97%. “This immunity is lifelong,” Handy said. “While an imported case in an international traveler may occur intermittently, spread within the US population should be preventable when we maintain herd immunity.” That’s why clinicians should actively encourage vaccination, said Tan, who is also an attending physician in the Division of Infectious Diseases at Ann & Robert H. Lurie Children’s Hospital of Chicago as well as a professor of pediatrics at Northwestern University’s Feinberg School of Medicine
“You have to use motivational interviewing techniques where you listen to why people don’t want to get vaccinated,” she explained. “Acknowledge that you hear what these individuals are saying, and then explain the facts: that measles is still present, and unvaccinated persons are much more likely to acquire the disease if they’re exposed.” In the US, “vaccination rates are decreasing below what is needed for population-level protection through herd immunity,” which requires about 95% of the population to be vaccinated, added Handy, an assistant professor of clinical pediatrics at the University of Pennsylvania’s Perelman School of Medicine. The CDC’s Morbidity and Mortality Weekly Report published in January 2023 showed that measles vaccination rates among kindergarteners for the 2021 to 2022 school year was only 93%. That worries Offit. “As more kindergarteners are starting to become exempt from school-mandated vaccines, measles could make a comeback,” he warned.
COVID-19 is partially to blame for the measles outbreak. Because of the pandemic, 61 million doses of measles vaccines were delayed or missed between 2020 and 2022, the CDC reported. “The measles vaccine, at some level, is a victim of its own success,” said Offit, who is also a professor of vaccinology at the Perelman School of Medicine. “I think people don’t see the disease, and so they don’t fear it.” As for the outlook for 2024, Handy wrote that, “it’s always challenging to predict how a disease will spread in a given year, but current vaccination rates of US kindergarteners raise concern that we will see increased outbreaks instead of isolated cases.” Although numerous reasons exist for low vaccination uptake, clinicians and public health authorities need to recognize that there isn’t a one-size-fits-all approach to increasing rates, Handy explained. “It takes a concerted effort to talk with patients and local communities to understand their specific hesitancies and design interventions specific to their needs,” she wrote. And most importantly, “a strong recommendation from a clinician for vaccination is one of the most impactful actions that can be taken to increase vaccination rates.”
Published JAMA Network (Feb. 28, 2024):
