What Is Causing the 2026 US Measles Outbreak? Vaccination Rates, Travel, and Immigration Examined

As measles infections continue to mount across the US and deaths are starting to occur, there is an increase in social media postings along with political appearances to shift the blame from federal policies, which discourage vaccine usage, to illegal immigration. The underlying thesis of these attacks is that the skyrocketing measles cases are due to a surge in illegal immigrants carrying the virus.

Representative Byron Donalds (R-FL) on Face the Nation (August 23, 2026) stated: “The reason why we have seen a measles outbreak in certain parts of the country is because of rampant illegal immigration into the US from the previous administration.” They stated that “People have come into the country illegally, have not had that vaccination schedule, and not the ones today on young kids that parents do have concerns about.”

However, it is hard to attribute the primary driver of the rise in measles cases in the US to illegal immigrants when the Trump Administration is touting immigration control of the border as “promises made, promises kept.” The White House states that “...the US had negative net migration in 2025—the first time in at least a half-century.” According to the WHO, the surge in measles cases in the US began in 2025 and increased in 2026 (Table 1).

As of September 10, 2026, the CDC has tallied 3,294 cases in the US. In my home state of Kentucky, there were no cases of measles in 2024, there were 13 in 2025, and 45 so far in 2026. The MMR (measles, mumps & rubella vaccine) immunization rate in Kentucky is 91%, short of the HP200 target of 95%, which is needed for herd immunity (Table 2).

Regardless of legal status, international travel has been an important source of measles outbreaks in the US. This was the case with the measles outbreaks in Orthodox Jewish Communities in New York and New Jersey in 2018-2019.

There are also outbreaks attributed to “migrants.” In March and April of 2024, there was a measles outbreak involving 64 confirmed cases in a Chicago migrant shelter.

However, the source of the large 2025 measles outbreak in West Texas (Gaines County) is unknown, and Texas’s Health Service Commissioner, Jennifer Shuford, MD, MPH, testified that she did not have “any data that would say yes or no” on whether immigrants caused the outbreak. Shuford also noted that measles vaccination rates had fallen, making the area a prime target for an outbreak. During this time, there were also 4 unrelated cases involving international travel.

As of Sept. 10, 2026, the CDC lists 38 new measles outbreaks this year. This includes 2 cases of measles at the Dilley immigrant family detention center, Texas, 7 cases in an Arizona ICE facility, and 14 cases at the Camp East Montana ICE detention center. These numbers are small compared to the total number of cases (3,294) and outbreaks (38) the US is experiencing so far this year.

Travelers to the US are encouraged but not required to receive vaccinations. In addition, vaccinations are also not required but recommended for US citizens who travel abroad and then return to the US. However, legal immigrants are required to receive a myriad of vaccinations, including measles.

Vaccination rates in many South American countries are higher than in the US. Unfortunately, vaccination rates in the US are declining. The percentage of US counties achieving the 95% measles vaccination rate required for herd immunity has dropped from 50% to 28%.

According to the World Atlas, the US ranks 103rd out of 192 countries in MMR vaccination, with a vaccination rate of 92%, well below the 95% threshold needed to achieve herd immunity. Our rates are below China, Cuba, Sri Lanka, Maldives, Nicaragua, Rwanda, Panama, Russian Federation, Bangladesh, Mexico, Argentina, Costa Rica, Chile, to name a few.

Twenty-seven countries are listed as having vaccination rates of 99%. Johns Hopkins Bloomberg School of Public Health reports the US measles vaccination rate (MMR) at 92%.

The gold standard for immunization tracking is the CDC, but unfortunately, the most recent data available is from 2022. At that time, more than 1 dose of MMR was reported at rates between 90.2% and 92.5%. Apparently, the CDC no longer tracks this data on a federal level. In January of 2026, the Centers for Medicare and Medicaid Services (CMS) stopped requiring states to report childhood vaccination rates. Medicaid covers about 49% of all children in the US.

In addition, vaccination rates across the US are not uniform; they vary widely. And those who do not believe in vaccinations often share common religious or political beliefs and tend to congregate with one another.

There is little doubt that diseases can enter through our border. The COVID-19 pandemic has taught us that borders are leaky, and the more infectious a virus is, the harder it is to prevent its entry into a country. With highly infectious diseases, even one person can cause a massive outbreak. Measles is the most infectious disease known to humanity, even more so than COVID-19.

Two years ago, measles was not a major issue in the US. Now, we are on the verge of losing our measles elimination status. Borders are leaky, and focusing on international travel is important. Still, it makes little sense to focus on illegal immigration as the primary driver of outbreaks during a time when illegal immigration is falling, and rates of measles are skyrocketing.

In addition, legal international travelers, both US citizens and foreign visitors, are not required to receive vaccination and too often have been documented as the source of measles outbreaks.

As I have repeatedly stated, we do not live in a fishbowl, which is why public health is so vitally important. Vaccinations are key to regaining our society’s measles protection. Our federal government needs to resume tracking vaccination rates and promote the highly effective, time-tested measles vaccine.