Measles is a highly contagious disease that was declared to be eradicated in 2000 in the United States because of widespread vaccinations. (Photo Credit: Centers for Disease Control and Prevention)

May 2 (UPI) -- Measles cases in the United States climbed to 939 in 29 states this year, the Centers for Disease Control and Prevention said Friday.

With the year only one-third over, the cases are the second most since 2000, when the disease was officially declared eliminated by the CDC.

The highest in 25 years was 1,273 in 2019 with 285 in 2024.

Six states are reporting outbreaks, meaning three or more related cases: Indiana, Kansas, Michigan, New Mexico, Ohio and Texas. The data include cases reported to the CDC as of noon Thursday.

Texas has a state-high 663, according to the Texas Department of State Health Services. Texas' vaccination rate is 94.3%. West Virginia is the highest at 98.3% and the worst is Idaho at 79.6%.

The deaths are two in Texas and one in New Mexico.

Weekly cases reported peaked on March 30 with 111 reported.

The Chicago area reported its first measles cases this week, one in a suburban Cook County resident with unknown vaccination status and another in an adult Chicago resident who traveled internationally and received one dose of the MMR vaccine, according to the Chicago Department of Public Health and Cook County Department of Public Health.

Among the cases this year, the CDC said about 96% are among unvaccinated people or unknown status. Conversely, 2% are among those who have received just one dose of the measles, mumps, rubella vaccine, and 2% among those who received the required two doses, according to the CDC.

Of the cases, 13% of patients have been hospitalized with most younger than 19 years old.

"This is a disease that was at the level of complete eradication; this should not be happening," Dr. Conrad Fischer, chief of infectious diseases at One Brooklyn Health in New York City, told ABC News. "It's very sad to have an enormously safe vaccine that has been used in billions of people and to have a sort of cultural societal amnesia about what these illnesses were like in the past."

Measles is the most contagious infectious disease known to humans, and is spread through the air by respiratory droplets produced by coughing or sneezing.

"For instance, tuberculosis will spread only to 2 or 3% of the people exposed," he said. "But if you are not vaccinated and you're exposed to someone with measles, you have a 90% chance of getting that infection."

Symptoms include cough, runny nose, inflamed eyes, sore throat, fever, and a red, blotchy skin rash. Over-the-counter fever reducers or vitamin A may help.

Six North and South Americas countries have reported 2,318 cases so far this year: U.S., Canada (1,069), Mexico (421), Argentina (21), Belize (1) and Brazil (5), have reported a total of 2,318 cases so far this year, according to World Health Organization.

Measles was declared eliminated from the U.S. in 2000 after the debut of the vaccination program, meaning there is no measles spreading within the country and new cases are only found when someone contracts measles abroad and returns to the country.

The measles vaccine was first licensed for public use in 1963, according to the WHO.

The first MMR vaccine was administered in 1971.

Before then, nearly every child got measles by the time they were 15.

The CDC estimates that 3 to 4 million in the U.S. were sickened by measles every year before the vaccine. That included 48,000 hospitalized and 400-500 deaths. Also, about 1,000 people suffered encephalitis, which is swelling of the brain.

US may have millions more measles cases over next 25 years