CDC Warns Vaccinated People Can Still Get Measles

By Zachary Stieber

The Centers for Disease Control and Prevention is warning people that even those who have received a measles vaccine can still contract the disease.

“Although vaccinated individuals are at low risk of acquiring measles, breakthrough infections can still happen,” the CDC said in a Feb. 2 post on X.

Dr. Ralph Abraham, the CDC’s new principal deputy director, wrote in a letter published Feb.1 in The Wall Street Journal that “although immunization coverage for measles is superior in the U.S. compared to peer countries, we can’t rely exclusively on vaccination.”

Officials pointed to a Jan. 29 report in the CDC’s quasi-journal that detailed how an unvaccinated person who lives outside of Colorado traveled through the Denver International Airport in 2025 while infectious with measles.

An investigation uncovered nine secondary cases and one tertiary case associated with the traveler’s international flight and time in the airport. Of those 10 cases, five occurred among people who had received two doses of the measles, mumps, rubella (MMR) vaccine before exposure, researchers with the CDC and health institutions in Colorado said. One other person may have received a vaccine in the past.

The CDC researchers said that the length of the flight and other factors contributed to transmission of measles from the traveler, “highlighting the risk for measles transmission from infectious travelers in both planes and airports and the value of ensuring that all eligible persons, particularly travelers, receive 2 doses of measles-containing vaccine to protect against measles.”

About 92.5 percent of kindergartners in the United States have received the MMR vaccine, according to the CDC. About 6.7 percent of babies in a recent large U.S. study had not received an MMR dose by their second birthday, researchers found. The CDC considers vaccine coverage of 95 percent in an area sufficient to provide herd immunity, or to generally prevent outbreaks.

The CDC on its website says that the best way to protect against measles is through MMR vaccination. Health Secretary Robert F. Kennedy Jr. has said measles vaccination is effective, and other officials kept two doses of measles vaccination on the childhood schedule when they recently downgraded recommendations for certain other shots.

The CDC estimates that one dose of the MMR vaccine provides 93 percent protection against measles, and a second dose raises that protection to 97 percent. The estimates are based on a 2013 paper published by the CDC that cites five earlier studies, including a 1999 study from the CDC, a CDC spokesperson told The Epoch Times previously.

A single dose does not trigger antibodies or immunity against measles, in all recipients, the CDC says in a publication called Pink Book. Approximately 2 to 7 percent of children who receive only one dose do not experience seroconversion, the publication states. After a second dose, more than 99 percent of recipients have antibodies.

The level of antibodies is lower than what people have following measles, but the immunity “appears to be long-term and probably lifelong in most persons,” the CDC says. While studies have found antibodies wane over time in at least some people, “this appears to occur rarely and to play only a minor role in measles transmission and outbreaks,” according to the CDC.

Waning immunity means that nearly 50 percent of school children can contract measles, nonprofit organization Physicians for Informed Consent says on its website. It cited, in part, a 2007 paper from the CDC that found antibodies declined from 0.2 percent following a second dose to 4.9 percent 10 years later.

Of the 588 cases recorded in the United States this year as of Jan. 30, 94 percent have been confirmed in people who were unvaccinated or have unknown vaccination status, the CDC says on another webpage. The agency has declined to provide a breakdown, splitting those categories into separate groups. The remaining 6 percent of cases were among vaccinated people.

In South Carolina, where the largest measles outbreak in the country is unfolding, officials say 90 percent of the 847 cases were among unvaccinated individuals. Six percent of the cases were among those with unknown vaccination status, and 4 percent were recorded among people who had received at least one MMR dose.

The number of measles cases in the United States shot to 2,267 in 2025, the highest since 1991.

Abraham said that the situation is not a U.S. policy failure.

“Under Health and Human Services Secretary Robert F. Kennedy’s leadership, the CDC has surged resources, including vaccines and therapeutics, nationwide to support state and local response efforts and contain outbreaks,” he said in his letter. “We are setting the global standard for public health.”

Officials also noted that many other countries, including Canada and Mexico, have reported higher case counts in total or per capita than the United States. Abraham described “porous borders with high regional caseloads.”

A spokesperson for the Department of Health and Human Services, Kennedy’s agency, told The Epoch Times in a Jan. 15 email that most cases in South Carolina are happening “in an under vaccinated immigrant community” and that the CDC is promoting treatments such as vitamin A to help with the outbreak.

Dr. Ferric Fang, a microbiologist at the University of Washington School of Medicine, wrote in a Feb. 2 post on BlueSky that he did not agree with Abraham.

“The resurgence of measles in North America not from ‘porous borders’. It is due to declining vaccine coverage,” he said. “Most cases are occurring in unvaccinated persons. All should have been preventable.”