The most recent outbreak of measles is threatening the United States' elimination status, according to a new Centers for Disease Control and Prevention (CDC) report published Thursday.
The first measles vaccine was introduced in 1963 and, thanks to a yearslong and highly effective vaccination campaign, the disease was considered eliminated from the U.S. in 2000, meaning it is no longer constantly present.
Despite occasional outbreaks, the U.S. has been able to maintain its elimination status. Cases have popped up due to international travel and unvaccinated or undervaccinated communities.
MORE: MMR vaccine rates are lagging amid a rise in measles cases. Experts blame a discredited study.However, the rapid increase in the number of measles cases during the first quarter of 2024 "represents a renewed threat to the U.S. elimination status," according to the CDC report.
As of April 11, 2024, there have been 121 cases of measles reported in the U.S. This is at least a 17-fold higher figure than the average number of cases seen during the same period from 2020 to 2023.
"What was surprising about 2024 is that we've seen a significant increase," said Dr. John Brownstein, an epidemiologist and chief innovation officer at Boston Children's Hospital and an ABC News contributor. "It's an alarming number because it indicates a trend going in the wrong direction for us, a virus that we have successfully controlled, a virus that we successfully have an effective vaccine for."
"We're seeing a rise that is unfortunate, and actually preventable, and so this outbreak highlights the fact that we are not unfortunately done with measles," he added.
This year, the number of measles cases have soared in part due to several localized outbreaks, including at a children's hospital and daycare center in Philadelphia, an elementary school in Florida and at a migrant center in Chicago.
Measles is so infectious that a measles patient can infect up to 90% of close contacts who are not immune.
Dr. Paul Offit, director of the Vaccine Education Center and an attending physician in the division of infectious diseases at Children's Hospital of Philadelphia, pointed out that almost all people in the U.S. who have had measles in recent years either traveled internationally to a country where measles has not been eliminated or were around someone who traveled internationally, and that immigrants are not responsible for the sporadic outbreaks.
He told ABC News that more than 20 years out since elimination status was declared, the U.S. should not be seeing as much of a renewed threat as it is.
"It's getting worse; I think it's fair to say that it is getting worse," Offit said. "Look, according to [the CDC's] definition. because there hasn't been 12 consecutive months of measles transmission, we're still considered to have eliminated measles ... but we're getting there."
This is not the first time that the measles elimination status has been at risk. In 2019, there were 1,274 reported cases due to outbreak in Washington state and in New York State and New York City.
MORE: Measles outbreaks are occurring in some pockets of the US. Here's why doctors are concernedThe new report comes as there has been a dip in routine childhood vaccinations. A CDC report in November found that exemptions for routine childhood vaccination among U.S. kindergartners are at their highest levels ever.
The report found that about 93% of kindergarteners received select routine childhood vaccines, including the measles, mumps, rubella (MMR) vaccine for the 2022-23 school year. This is about the same as the previous school year but lower than the 94% seen in 2020-21 school year and the 95% seen in the 2019-20, prior to the COVID-19 pandemic. The latter percentage had been the standard for about 10 years.
Offit said there is a critical percentage of parents choosing not to vaccinate their children with the MMR vaccine. There are various reasons, including vaccine hesitancy from the COVID-19 vaccine affecting the choice to receive other vaccines and not remembering how serious measles used to be prior to vaccines.
In the decade prior to the first measles vaccine in 1963, there were three to four million cases annually, which led to 48,000 hospitalizations and 400 to 500 deaths.
"The misinformation about measles out there is, 'Oh, everybody used to get measles and recover. What's the big deal?'" Dr. William Schaffner, a professor of preventive medicine at Vanderbilt University Medical Center, told ABC News. "And unfortunately, that does not convey the seriousness of measles infection. Even uncomplicated measles made children miserable."
He explained that measles could lead to several complications including conjunctivitis, or pink eye; light sensitivity; pneumonia; and encephalitis, or inflammation of the brain.
Experts said it's important for pediatricians to speak to parents about their fears regarding the vaccine.
"Number one is to find out what it is that's causing them to choose not to vaccinate, what's the fear, because the fear can invariably be addressed with information," Offit said. "I think it's understandable how people can be hesitant to get a vaccine, but it is a dangerous game we play. I mean, it's a game of Russian roulette."
Despite the outbreak, the experts and the CDC say that anyone who has had a previous measles infection or who has received two doses of the MMR vaccine is essentially protected for life.
The CDC currently recommends receiving two doses of the MMR vaccine, with the first dose at 12 to15 months old and the second dose between ages 4 and 6. One dose of the measles vaccine is 93% effective at preventing infection if exposed to the virus. Two doses are 97% effective, according to the CDC.
"We've had a vaccine that has been in use for a very long time and is shown to be incredibly effective in keeping our elimination status of measles going," Brownstein said. "But it's not about the vaccine itself. This is not a question of whether the vaccine works. This is a question of whether people work to get the vaccine."
The CDC also emphasized in the report that the vaccine should be given before international travel.
"That's a new emphasis, and I hope that that information gets out to providers and through the providers, to the parents, so that even if you've withheld your child from vaccination, domestically, if you wish to get on a plane and go internationally, that should be an indication for you to get your child vaccinated," Schaffner said. "You do not want your precious child to have to go through a measles infection. I guarantee it."