Fact Check: Is Byron Donalds’ claim illegal immigration caused US measles outbreaks true?

WASHINGTON, DC: As measles cases rise across the US, health experts point to declining measles, mumps and rubella (MMR) vaccination rates as a major factor behind the outbreaks.

Amid the tension, Republican Florida gubernatorial candidate Byron Donalds has blamed illegal immigration during the Biden administration for measles outbreaks in parts of the country. Donalds said “rampant illegal immigration” was the reason for the outbreaks. Let's fact-check the claim.

Claim: Byron Donalds blamed illegal immigration for measles outbreaks

During an August 23 appearance on CBS News’ 'Face the Nation,' host Margaret Brennan noted that Florida's measles vaccination rate is below the level needed for herd immunity.

She then asked Byron Donalds whether he would advise Florida parents to vaccinate their children.

Donalds said, "No, actually my message to Floridians and, quite frankly, to Americans is the reason why we have seen a measles outbreak in certain parts of the country is because of rampant illegal immigration into the United States from the previous administration."

Donalds claimed that people who entered the US illegally had not followed the recommended measles, mumps and rubella (MMR) vaccination schedule. He argued, "So the key thing is, you number one, you got to control immigration into your country. You can’t have an entire segment of people, more than 10 million, coming to your country without that vaccination schedule.”

Fact Check: No evidence supports the claim

The claim is false. There is no evidence that illegal immigration caused measles outbreaks in the US.

It is also wrong to say that more than 10 million immigrants entered the US illegally during Joe Biden’s presidency.

The Biden administration released about 4.3 million people into the US while they waited for immigration court hearings. That figure does not mean all of them entered the country illegally or that they were all unvaccinated.

Infectious disease experts reported that declining measles, mumps and rubella (MMR) vaccination rates in the US are the main reason measles outbreaks have grown. About 94% of confirmed measles cases in 2026 involved people who were unvaccinated or whose vaccination status was unknown.

The 2026 measles outbreak has already surpassed the record number of cases reported in 2025, which was the highest annual total since 1991. Measles is highly contagious and can cause serious complications, including pneumonia, brain swelling, and death.

The CDC recommends two doses of the MMR vaccine. The two-dose series is about 97% effective at preventing measles infection. The CDC does not track the immigration status of people who contract measles in the US. Because of this, no data show that people who entered the country illegally caused the recent outbreaks.