美国麻疹病例为何激增至35年来最高水平Why US Measles Cases Have Surged to a 35-Year High

Thanks to the introduction of a vaccine in 1963, measles was declared eliminated in the US in 2000. Now the highly contagious disease has reemerged as a threat as declining vaccination rates fuel outbreaks around the country. Measles cases have now reached a level not seen in more than three decades.

The US Centers for Disease Control and Prevention on Nov. 6 reported 5,182 confirmed infections so far in 2026, the most since 1991. Eight people have died, according to state reports, across Pennsylvania, New York and Wisconsin. The vast majority of cases have been among unvaccinated people.

Outbreaks of measles have become more common as the share of Americans who are unvaccinated against childhood illnesses has increased. That’s largely been driven by persistent and unfounded beliefs that immunizations, particularly the measles, mumps and rubella (MMR) shot, are dangerous and unnecessary. For the 2025-2026 school year, measles vaccination rates fell to 92.4% for kindergarteners, according to the CDC. A 95% immunization rate of two doses is needed to stop measles’ spread and protect people who cannot get a vaccine; the last time the immunization rate reached that level was in 2020.

Falling immunization rates exacerbated by pandemic-related disruptions also have fueled a worldwide resurgence of measles, halting years of progress. Since 2020, global measles cases have risen more than threefold, while cases of rubella, another contagious viral infection, have more than doubled. Worldwide, only about three-quarters of children have received the recommended second dose of the MMR vaccine, the World Health Organization warned in July.

Pennsylvania has been the hardest-hit state, with 1,505 reported infections in 2026 as of Nov. 9. The state’s outbreak is concentrated in Lancaster County, home to the nation’s biggest Amish community and a large Mennonite population. About 45 states have reported at least one measles case to the CDC, and there have been 43 new outbreaks this year, defined as three or more related cases.

The CDC recommends vaccination as the best way to protect against measles. And some state and local health officials have encouraged citizens to stay up to date on measles immunizations.

At the same time, President Donald Trump’s administration has pulled back on broad support of immunizations. Robert F. Kennedy Jr., the nation’s top health official, at times has downplayed the threat of measles in public statements and has incorrectly linked the measles vaccine to autism.

In 2025, Kennedy removed all the members of a CDC advisory panel on immunizations and added vaccine critics. The revamped panel created a subcommittee to review the long-established childhood and adult vaccination schedule, which includes measles vaccines. The advisory panel makes critical recommendations for vaccines that dictate which are covered by insurance and which will be offered for free under the federally funded Vaccines for Children program. The changes to the committee have been challenged in federal courts.

In August, Trump signed an executive order seeking to split up the MMR vaccine into three separate shots — a move that would be time-consuming and costly for drugmakers. Trump called the combined MMR shot “quite lethal” at theg, though there’s no such evidence.

In a statement, the Department of Health and Human Services said Kennedy and CDC Director Erica Schwartz continue to endorse the MMR vaccine as the most effective way to prevent measles. The agencies “will continue working with states to stop transmission, close vaccination gaps, strengthen outbreak response, and protect Americans from measles.”The CDC had acknowledged only four measles fatalities in 2026 as of Nov. 6, in contradiction with state reports of eight deaths. The agency said it is investigating the others and working to determine what defines a measles death with an outside group of epidemiologists.

Globally, public health authorities fear they won’t be able to adequately monitor and respond to the measles threat. The WHO warned that its largest global laboratory network would collapse unless new funding was secured to replace the support lost after an order by Trump to withdraw the US from the United Nations agency.

People who have had two doses of either the MMR or MMRV (measles-mumps-rubella-varicella) vaccine are considered up to date. Most people born before 1957, when measles was widespread, are presumed immune due to natural exposure. However, those who received the inactivated measles vaccine between 1963 and 1967 — rather than the more effective live vaccine — might need a booster.

Measles is one of the world’s most contagious viruses, infecting the respiratory tract before spreading throughout the body. Nine out of 10 unvaccinated people will get the virus if they are exposed to someone who has it. Measles causes fever and a rash, and in severe cases, can lead to complications such as deafness, blindness, pneumonia and encephalitis — swelling of the brain that can be fatal — and the loss of immunity to other diseases.

About one in five unvaccinated people infected with measles will require hospitalization. In 2026, about 11% of people with measles have been hospitalized, according to the CDC.

In 2024, there were an estimated 11 million cases worldwide and 95,000 deaths, according to the WHO, mostly among unvaccinated or under-vaccinated children below the age of 5.

Measles is especially dangerous for babies, older people and those with suppressed immune systems, such as cancer patients receiving radiation or chemotherapy. Measles during pregnancy can lead to miscarriage, early delivery and low birth weight. It can also weaken the immune system for years by attacking B cells, which are crucial for helping the body fight off diseases. In rare cases, the infection can linger in the brain, causing a fatal disease years after the initial exposure.

People can catch measles just by being in the same room where an infected person has breathed, coughed or sneezed within two hours. An individual can spread the disease unknowingly before showing any signs or symptoms.

No. Some parents might believe that the vaccine causes autism because signs of the developmental disorder typically appear around the same time that children are recommended to receive the first dose of the measles vaccine, at roughly 1 year of age. But the idea that the vaccine is linked to autism is based on a 1998 study that turned out to be fraudulent. It was retracted and its author, Andrew Wakefield, was stripped of his UK medical license for “dishonest” and “irresponsible” work. Repeated studies have debunked any connection between autism and vaccines.

The MMR vaccine is extraordinarily safe. The vaccine is 93% effective against the virus after one dose and 97% effective after two doses, making it a crucial public health tool.

Potential side effects include a sore arm from the shot, fever, a mild rash and temporary joint pain and stiffness, mostly among teenage or adult women not already immune to rubella. The MMR vaccine has been linked with a very small risk (four cases in every 10,000) of seizures caused by a spike in temperature that have no long-term effects. Serious allergic reactions are extremely rare but have been experienced by patients allergic to neomycin, as the vaccine contains a small quantity of the antibiotic. They should avoid the vaccine, according to the CDC.

There is no specific treatment for measles. Medical care is aimed at addressing symptoms while the virus runs its course, which typically takes seven to 10 days. Acetaminophen may relieve fever and muscle aches. Rest will boost the immune system. Six to eight cups of water a day will help with hydration. A humidifier can ease a sore throat and cough. After contracting measles, a person is almost always immune for life.