Measles Outbreaks Reported in Multiple States: What to Know

Measles is an airborne virus that can stay in the air for two hours and can be acquired by touching contaminated surfaces or inhaling the virus in the air. According to the CDC, nine out of 10 people who have not been immunized against the measles virus will become infected after exposure. The symptoms of measles include:

• Cold or flu-like symptoms
• Red eyes
• Fever
• Red or reddish-brown rash across the entire body
• Spots inside the mouth

“Measles is extremely contagious and there has been an increase in measles cases around the world (with a million more measles cases reported in 2022 than 2021 by the WHO) due to setbacks in measles vaccination rates during the COVID-19 pandemic,” Dr. Monica Gandhi, MPH, a professor of medicine at the University of California San Francisco’s Division of HIV, Infectious Diseases, and Global Medicine, told Healthline. “Members of the public are at risk if they have not been vaccinated (which usually happens in childhood) so the larger population need not be concerned if vaccinations are kept up to date.”

In the last half of 2023, there were more than 20,000 cases of measles in Yemen, the country with the leading outbreak. This is an indicator that without widespread immunity or vaccination, the virus can spread widely, Dr. Tina Tan, an attending physician at Division of Infectious Diseases at the Ann & Robert H. Lurie Children’s Hospital of Chicago, told Healthline.

“There are multiple countries around the world where measles is endemic and circulates widely in the community,” Tan said. “With international travel on the increase, unimmunized individuals are getting exposed to measles in the foreign countries that they are visiting, they are getting sick and exposing unimmunized, under immunized and persons that are too young to be immunized or who are unable to be immunized for medical reasons to measles. This has been reported on a number of occasions where exposure is occurring on airplanes, in airports or in the unimmunized person’s community.”

The combination of reduced vaccine rates from the early pandemic years and a backlash against vaccines in general by some parents are likely contributors to this uptick in measles, which had been essentially eliminated from the general U.S. population for years. In Mississippi, for example, nearly 99% of kindergartners received both MMR in 2021-22 — the highest rate in the nation. But a U.S. District Court judge in 2023 allowed parents there to file for religious exemptions to state-mandated vaccines, and it appears that similar trends have occurred in other states.

“There are reduced rates of childhood vaccination in the US, with a record number of applications by parents for exemptions to mandatory vaccination at school (reported by the CDC in November 2023),” Gandhi said. “Therefore, young children who have not yet been vaccinated (vaccination starts at 12-15 months) or whose parents decline to get them vaccinated are most at risk of measles infections.”

Unlike the recent increases in respiratory infections around the U.S., these measles outbreaks are not a result of any type of seasonal patterns, Tan said.

“The surges that we are seeing are due to a decline in MMR immunization rates, so that there are more people that are unimmunized and do not protective immunity,” Tan said. “Measles is one of the most highly contagious infectious diseases with the attack rate in a susceptible individual exposed to measles being 90% in close contact setting. Population immunity needs to be 95% or greater in order to stop ongoing transmission in the community.”

Vaccination against measles is extremely effective and safe. The World Health Organization estimates that between 2000 and 2021, 56 million deaths were prevented because of the vaccine. Children typically don’t receive the first dose of vaccine until they are a year old, with a second dose typically between the ages of 4 and 6. For adults who have not been vaccinated, getting the shot is ultimately the strongest defense.

“There is no evidence that face masks have any effectiveness against the small measles virus; ventilation is likely to minimize the risk of any pathogen spread by a respiratory route. The measles vaccine is a live, attenuated vaccine (developed in 1965) given in conjunction with live vaccines for mumps and rubella (e.g. MMR vaccine),” Gandhi said. “Natural infection confers lifelong immunity and the strength of protection from two vaccine doses (which confers 97% protection) is long, although adults should receive a booster MMR vaccine during an outbreak.”

“For those persons who are unimmunized who have been exposed to measles including those that for medical reasons are unable to be vaccinated, they should be quarantined at home and not attend school, daycare or be in a healthcare setting for at least 21 days after the onset of rash in the last case of measles reported in the setting where they were exposed,” Tan added.

Given that these surges are not seasonal, and how infectious the virus that causes measles can be, widespread vaccination is the most effective tool any population has to return to a status the U.S. had in 2000, when the WHO declared measles “eliminated” in the country.

“The level of immunity to measles in the general population in the U.S. is quite high given high vaccination rates (given in childhood since the 1960s) with high natural infection rates prior to the 1960s,” Gandhi said. “However, population immunity will decline if these childhood vaccination rates in the U.S. to measles do not improve. Young children should receive two doses and adults may require booster vaccination prior to international travel, prior to college, prior to pregnancy or during outbreaks.”

An increase in measles infections in several U.S. states is an indicator that immunity and vaccination rates have dropped.

The best defense against measles, doctors and health officials say, is getting vaccinated against the virus.

Children under the age of 1 cannot usually be vaccinated, but after that it’s recommended that they get both doses of the vaccine.