Measles outbreaks in Florida and Philadelphia have come as parents defied advice to quarantine their children and at least one high-profile state official sowed confusion about how long to keep unvaccinated children out of school.

Both the outbreaks in Broward county, Florida, and Philadelphia made news after children brought the disease into the wider community. Six children grew sick at Manatee Bay elementary in Florida, and nine in Philadelphia after a child went to a daycare while infected.

“It’s a worrisome disease for a number of reasons, so I’m worried,” said 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 (Chop). Offit is also the recent author of Tell Me When It’s Over: An Insider’s Guide to Deciphering Covid Myths and Navigating Our Post-Pandemic World.

In Philadelphia, a measles outbreak in January was caused when a seven-month-old infant contracted the disease while traveling abroad and, contrary to the advice of doctors at Chop including Offit, was brought to daycare.

In Florida, a third-grade student with no history of international travel was diagnosed with the disease and spread it to other students. Less than 92% of children in Broward county had received recommended immunizations against diseases such as measles. The Center for Disease Control and Prevention’s (CDC) considers 95% the immunization threshold to prevent outbreaks.

Florida’s surgeon general, Joseph Ladapo, a well-known Covid-19 vaccine skeptic appointed by the Republican governor, Ron DeSantis, further disrupted efforts to contain the disease in when he told parents they could ignore the CDC’s advice to keep unvaccinated children home for 21 days. Ladapo sent a letter to parents saying he “is deferring to parents or guardians to make decisions about school attendance”.

Side effects from the measles vaccine are rare, usually transient and not serious. The disease itself, however, can have very serious consequences, including rare neurological infections and death. Roughly one to two children per 1,000 infected will die of the disease or its complications, according to the CDC. In rare cases, serious conditions can emerge years later.

Describing measles symptoms, Offit said: “the rash starts at the hairline and spreads to the face … It’s like you sort of had a bucket of rash poured on your head,” which spreads down the body.

“It’s invariably associated with cough, conjunctivitis and runny nose,” Offit said, adding, “and kids are sick – they look sick, they’re miserable.”

A child of the 1950s, Offit was infected with measles himself (the first vaccine was introduced in 1963), and has personally treated cases of neurological devastation related to measles infections.

Since the mid-20th century, measles vaccination in the US has been so successful that some doctors have never even encountered the disease. Measles was eliminated in the US in 2000. It has since re-emerged alongside vaccine misinformation.

Notably, Offit said that when he worked on the team treating the infant with measles in Philadelphia, he was the sole doctor who had seen a case of the disease. He believes vaccines have been so successful that few people remember what it was like to live with measles.

In addition to immediate risk of death from measles, a rare condition called subacute sclerosing panencephalitis can manifest years later. The progressive neurological disorder lies dormant for six to eight years before symptoms emerge, usually including personality and behavior changes, disturbances in motor functions and blindness. Most children diagnosed with the disease will die between one and three years later. Offit has treated three such cases in his career.

In 2024, the CDC had received 20 cases of measles by mid-February – marking a return to a pre-pandemic pattern of a few dozen cases per year, before a major outbreak in 2019.

That year, the US suffered the worst measles outbreaks in roughly 25 years. The Centers for Disease Control and Prevention (CDC) identified 1,274 cases of measles, many spread through under-immunized communities who had been targeted with vaccine misinformation. Among them, 474 cases were identified in New York in the orthodox Jewish communities in New York City and suburban Rockland county.

Those cases were entirely eclipsed in 2020 by the Covid-19 pandemic. Restrictions on social gatherings and widespread mask use nearly eliminated non-Covid-19 respiratory diseases that year, including measles, influenza and respiratory syncytial virus, better known by its acronym RSV.

But many of the factors that allowed cases to spread in 2019 have now returned, and some have worsened. A November 2023 report by the CDC found national vaccine coverage for state-required vaccines decreased from 95% in 2019-2020 to 93% in 2021-2022. It remained flat at 93% in 2022-2023.

During the same time period, the number of children who claimed exemptions from state vaccine mandates also increased by 0.4% in 2022-2023 to 3% of all children, and increases happened in 41 states.

What’s more, much like in New York in 2019, those decreases in vaccine uptake were clustered. Hawaii saw a precipitous 7.9% decline in uptake of the measles, mumps and rubella (MMR) vaccine between 2022 and 2023, and lower but still alarming declines in polio, varicella (chickenpox) and the diphtheria, tetanus and acellular pertussis vaccines (DTaP).

The last recorded measles death in the US was of a 28-year-old Washington woman named Catherine Montantes. Montantes, who was vaccinated, died in 2015 after she was exposed to measles in the waiting room of a local clinic. She suffered from an autoimmune disorder, which made her immune system less sensitive to the measles vaccine.

Two doses of the measles vaccine is 97% effective against the disease, meaning even vaccinated people can contract the disease if it is allowed to spread in an undervaccinated community.

“Vaccines are a victim of their own success,” said Offit. “Don’t mess around with this disease, this is not a disease you want to relive”.