Fact-check
Measles, Migration, and the Missing Evidence
Donalds blamed Biden-era immigration for the 2026 measles surge. CDC data: 16 of 2,903 cases involved international visitors. The cause is declining vaccination.
By The Crosscheck Desk · 2026-09-02
La 'inmigración ilegal desenfrenada' durante la administración Biden es la causa de un brote de sarampión en ciertas partes de EEUU.
Hubo un brote de sarampión en ciertas partes de EEUU.
Rampant illegal immigration during the Biden administration caused a measles outbreak in certain parts of the country.
The Statement
On August 23, 2026, Rep. Byron Donalds (R-FL), Florida's Republican gubernatorial nominee, appeared on CBS News's Face the Nation and offered an explanation for the country's measles surge: "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."[1]
The claim assigns a specific cause (undocumented immigration under President Biden) to a confirmed and serious public health event. His campaign declined to provide supporting data when contacted by PolitiFact.[2]
The statement contains two separable questions: Was there a measles outbreak? And did illegal immigration cause it? The evidence answers each differently.
Claim: Was There a Measles Outbreak?
"Hubo un brote de sarampión en ciertas partes de EEUU." / "There was a measles outbreak in certain parts of the country."
The outbreak is confirmed. As of August 27, 2026, the CDC had recorded 2,903 measles cases in the United States, a 35-year high.[3] This surpasses the full-year 2025 total and every other year since the disease was declared eliminated in 2000. Outbreaks were active across 47 states plus the District of Columbia, with 37 separate outbreak clusters identified by mid-August.
as of Aug. 27, 2026
since 1991
with active cases
South Carolina's outbreak alone reached 997 cases before ending in April 2026, the nation's largest measles cluster since elimination was declared. Utah's separate outbreak surpassed 500 cases and remained active through August.[4] The outbreak threatens the U.S. measles elimination status maintained since 2000.
Claim: Did Illegal Immigration Cause the Outbreak?
"La 'inmigración ilegal desenfrenada' durante la administración Biden es la causa de un brote de sarampión en ciertas partes de EEUU." / "Rampant illegal immigration during the Biden administration caused a measles outbreak in certain parts of the country."
What the CDC data show
The CDC does not track immigration status in measles case reports. Among 2,903 confirmed 2026 cases, 16 involved international visitors: people who entered the U.S. on a foreign passport and contracted or transmitted measles here. That is 0.55% of all confirmed cases.[3] The remaining 2,887 were among U.S. residents.
The agency's framing is explicit: measles enters through international travel, primarily via unvaccinated Americans going abroad. Outbreaks grow when the virus reaches communities with insufficient herd immunity, meaning communities where fewer than 95% of residents are vaccinated.
Approximately 94% of confirmed 2026 cases involved individuals who were unvaccinated or whose vaccination status was unknown.[1]
What experts say
Dr. William Schaffner of Vanderbilt University told PolitiFact that "the very substantial majority" of cases stem from unvaccinated Americans traveling abroad and returning to their communities.[1] Dr. Paul Spiegel of Johns Hopkins stated the principle directly: "Movement does not by itself create an outbreak; susceptibility does."[2] Dr. George Rust of Florida State University, a former county health director, described the documented pattern: "The typical scenario is that a U.S. citizen goes overseas for a vacation or a mission trip" and returns to spread the virus.[5]
The countries-of-origin vaccination picture
If undocumented migrants from Central America and Mexico were a primary introduction source, the expected pattern would show measles flowing from countries with low MMR vaccine coverage. The data do not support this. Mexico, Guatemala, and Honduras each include the MMR vaccine in their routine national childhood vaccination schedules. Measles is surging across the Americas in 2026, but that surge traces to domestic vaccination gaps in each affected country, not to populations exporting the disease to the U.S.[14] Mexico's 2025-26 outbreak itself did not export the virus northward. The reverse happened: an unvaccinated nine-year-old from a Mennonite community in Seminole, Texas traveled to Chihuahua, Mexico, and sparked Mexico's outbreak.[9]
Where the Outbreaks Actually Started
The documented origins of the three largest 2026 U.S. outbreak clusters each trace to unvaccinated American residents:
- Ave Maria University, Collier County, Florida: Over 100 cases at this Catholic liberal arts university near Naples. The outbreak was traced to an unvaccinated student who traveled out of state during a holiday break. The university requires proof of MMR vaccination but accepts signed waivers under Florida law. No connection to undocumented immigration was identified in contact tracing.[7]
- Amish and Mennonite communities (Pennsylvania, Ohio, Indiana, Texas): These communities maintain historically low vaccination rates based on religious conviction. When measles enters through a returning traveler or visitor, it spreads through the unvaccinated population. This pattern has recurred in these communities across multiple outbreak years, independent of any immigration trend.[8]
- South Carolina (997 cases, largest single outbreak since elimination): The outbreak ended April 26, 2026 after spreading through communities with below-average kindergarten MMR coverage. Health officials traced introductions to domestic travelers, not border crossings.[4]
The frame-lock problem in Donalds' claim is this: it attributes the outbreak to a single cause (immigration) while the documented evidence points to a different cause (domestic vaccination gaps). The more productive question is why vaccination coverage among American children has fallen below the threshold needed to stop measles, and what policies have contributed to that decline.
Who Is Involved and What Is at Stake
| Actor | Role in This Situation | Stakes |
|---|---|---|
| Byron Donalds | FL gubernatorial nominee; made the causal claim | Claim is false. Campaign declined to provide supporting data. Florida's largest outbreak (Ave Maria) traced to unvaccinated American students, not immigrants. |
| Undocumented immigrants | The accused cause | Bearing political blame for a crisis the data do not support they caused. Countries of origin maintain routine MMR vaccination. |
| Unvaccinated American communities | Primary outbreak locus | At highest risk of continued spread. Includes students with religious waivers, Mennonite/Amish communities, children of vaccine-hesitant parents. |
| CDC and state health departments | Tracking and responding | Operating under conflicting federal health messaging while U.S. elimination status faces formal review in November 2026. |
| HHS / federal health leadership | Oversees vaccination policy and messaging | Conflicting public signals on vaccine safety from senior officials have contributed to hesitancy at a critical period. |
| The vaccinated public | Bystanders at rising risk | As community coverage falls and elimination status weakens, even vaccinated individuals face elevated exposure risk in low-coverage areas. |
The Strongest Case for the Immigration Argument
The argument that immigration contributes to disease spread is not without historical foundation. Large-scale population movements can introduce pathogens to communities with no prior exposure. In 2019, a measles outbreak in New York City had partial roots in returning travelers from regions with active outbreaks. If undocumented migrants were entering from countries with high measles burden and low MMR coverage, the arithmetic of outbreak risk would change. Detention facilities with overcrowding and poor vaccination-record tracking are genuine epidemiological risk environments. People crossing borders outside official channels may lack access to routine childhood vaccination, depending on the conditions of their upbringing.
This argument earns a score of 2 out of 5 against the core finding. Here is why it does not flip the verdict: First, the documented introduction mechanism in 2026 is unvaccinated Americans traveling abroad, not migrants entering the country. Second, the top countries associated with undocumented immigration (Mexico, Guatemala, Honduras) maintain routine MMR childhood vaccination; Mexico's 2026 outbreak originated from an American visitor, not from migrants arriving in the U.S. Third, the 16 international-visitor cases out of 2,903 total (0.55%) represent a negligible documented share, and that figure covers all international travel, not just undocumented border crossings. The steelman holds as a theoretical future-risk framing; it does not describe what happened in 2026.
The Documented Cause: Declining Vaccination
Measles has one of the highest transmission rates of any known pathogen. Its R0 (the average number of people one infected person infects) ranges from 12 to 18. Interrupting that chain requires that more than 95% of a community be vaccinated, a threshold called herd immunity. Below that threshold, pockets of unvaccinated people become outbreak fuel the moment the virus arrives.
That threshold is what the U.S. has been losing:
- MMR vaccination coverage among U.S. kindergartners fell from 95.2% in the 2019-2020 school year to 92.4% in 2025-2026, a drop of 2.8 percentage points.[10]
- The 92.4% figure sits below the 95% minimum. An estimated 280,000 kindergartners were below the immunity threshold in 2025-2026.[10]
- Nonmedical vaccine exemptions rose from 1.9% in 2020-2021 to 4.2% in 2025-2026, a 121% increase over five years.[11]
- Only 10 states maintained MMR coverage at or above 95% in 2025-2026. In 24 states, exemption rates exceeded 5%. In 11 states, they exceeded 7%.[11]
The timing of this decline matters. It accelerated during a period when prominent federal health voices publicly questioned vaccine safety and efficacy. Messaging from senior officials at the Department of Health and Human Services in 2025-2026 created confusion about MMR recommendations, a documented contributor to hesitancy at the precise moment the U.S. needed coverage to hold at 95%.[12]
The outbreak's geography aligns with the coverage map. States with the heaviest case loads are also states where kindergarten MMR coverage has fallen furthest or where nonmedical exemption rates are highest. That correlation does not appear in the relationship between measles cases and immigration patterns.[13]
What's at Stake: Measles Elimination Status
The U.S. declared measles eliminated in 2000. Elimination does not mean zero cases. It means the virus no longer circulates continuously within the country; any introductions die out before establishing endemic spread. The U.S. has maintained that status for 26 years.
A key criterion for elimination is that no single outbreak persists beyond 12 months of continuous transmission. An outbreak in the Utah-Arizona border region has now crossed that threshold. The Pan American Health Organization (PAHO) is scheduled to evaluate U.S. elimination status in November 2026.[6]
Losing elimination status would be a formal, internationally recognized public health setback, the first since the designation was achieved. It would carry practical consequences: renewed vaccination requirements for international travel, additional scrutiny of U.S. public health infrastructure, and a reset on the epidemiological clock that has measured U.S. measles control since 2000.
The causation Donalds attributes to immigration is relevant here in a different sense. The decision about how to address the outbreak will be shaped by the political explanation that dominates. An immigration-based frame directs policy attention toward border enforcement. A vaccination-based frame directs it toward exemption policy, school requirements, and public health messaging. Only one of those frames matches what the data show is driving the outbreak.
What to Watch
- PAHO elimination review, November 2026. International health officials will assess whether the U.S. can still claim measles elimination status. The Utah-Arizona outbreak's duration is a key threshold in that assessment. A loss of status would be the most concrete measurable consequence of the current outbreak.
- Full-year 2026 CDC case total. If the year closes above 3,000 cases, it will mark two consecutive record-setting years. That milestone will inform the federal and state legislative response entering 2027.
- Kindergarten exemption data for 2026-2027. The CDC's annual school-year vaccination report will indicate whether the exemption rate continues rising beyond 4% or begins to plateau. This is the clearest leading indicator of outbreak risk for the next cycle.
- Florida vaccination exemption policy. Florida's Ave Maria outbreak traced to students using state-law waivers. Donalds is now the Republican gubernatorial nominee. His position on those waivers, should he win in November 2026, will bear directly on the state's outbreak risk.
What was said?
On August 23, 2026, Rep. Byron Donalds appeared on CBS News and said: "The reason why we have seen a measles outbreak in certain parts of the country is because of rampant illegal immigration." Donalds is a Florida congressman running for governor. He blamed immigration under President Biden for the measles surge. This statement makes two claims. We checked both.
Claim 1: Was there a measles outbreak? — True
Yes. As of August 27, 2026, the U.S. had 2,903 confirmed measles cases. That is the highest number since 1991. The disease had been under control for over 20 years.
Outbreaks spread to 47 states. South Carolina had the worst single outbreak in decades: 997 cases before it ended in April 2026. Utah had over 500 cases.
Claim 2: Did illegal immigration cause the outbreak? — False
The CDC tracked who got measles. Of 2,903 cases, only 16 (less than 1%) were in international visitors. The other 2,887 cases were in people who live in the United States.
The CDC says measles usually enters the U.S. when an unvaccinated American travels abroad and comes home sick. Then it spreads to others who are not vaccinated. About 94% of all 2026 cases were in people who were not vaccinated, or whose vaccine history was unknown.
Where did the outbreaks actually start?
- Ave Maria University, Florida: Over 100 cases. It started with an unvaccinated student who traveled out of state during a holiday. No connection to immigration was found.
- Amish and Mennonite communities: These groups in Pennsylvania, Ohio, Indiana, and Texas avoid vaccines for religious reasons. The virus entered through a traveler and spread through their communities.
- South Carolina: The large outbreak spread through areas with low vaccination rates. Officials traced it to domestic travelers, not border crossings.
One striking fact: Mexico's measles outbreak did not spread to the U.S. It was the other way around. An unvaccinated child from a Texas community traveled to Mexico and started Mexico's outbreak.
Who is involved and what is at stake?
- Byron Donalds: His claim is false. The biggest Florida outbreak happened among unvaccinated American students, not immigrants.
- Undocumented immigrants: They are being blamed, but the evidence does not support it. Mexico, Guatemala, and Honduras all give the MMR vaccine to children as part of their normal health programs.
- Unvaccinated Americans: These are the people driving the outbreak. This includes children with religious exemptions, students using waivers, and communities that avoid vaccines.
- The U.S. health system: Officials are trying to respond while some federal leaders have sent mixed messages about vaccines, making the problem harder to address.
The strongest argument for the immigration claim
Large numbers of immigrants can sometimes bring disease. This has happened in history. If migrants came from places with high measles rates and low vaccination, the risk would increase. But this does not match the 2026 facts. Only 16 of 2,903 cases involved international visitors. The main countries people cross from illegally (Mexico, Guatemala, Honduras) all vaccinate children against measles. And Mexico's outbreak came from the U.S., not the reverse. The argument describes a theoretical risk, not what happened in 2026.
The actual cause: fewer Americans are getting vaccinated
Measles is extremely contagious. To stop it from spreading, at least 95% of a community needs to be vaccinated. This is called herd immunity. When fewer people are vaccinated, the virus finds unprotected people and spreads fast.
- In 2019-2020, 95.2% of kindergartners had their measles vaccine.
- By 2025-2026, that number fell to 92.4%. About 280,000 children were unprotected.
- Parents skipping vaccines for personal or religious reasons: that rate more than doubled, from 1.9% in 2020-2021 to 4.2% by 2025-2026.
This happened at the same time some federal health officials publicly questioned vaccine safety, which confused many families.
What is at stake: could the U.S. lose its measles-free status?
The U.S. declared measles eliminated in 2000. That means the virus no longer circulates freely in the country. The U.S. has held this status for 26 years.
There is now a serious risk of losing it. A health body called PAHO will review U.S. status in November 2026. If an outbreak has lasted more than 12 months without stopping, the U.S. could lose the eliminated designation. An outbreak in Utah and Arizona has already crossed that mark.
What to watch
- November 2026: PAHO meets to decide if the U.S. still counts as measles-eliminated.
- End of 2026: The CDC will release the full-year case total. Passing 3,000 would mean two record-breaking years in a row.
- 2027: New data on how many kindergartners skipped vaccines will show if the problem is getting better or worse.
- Florida: Donalds is running for governor. Florida law allows vaccine waivers. The Ave Maria outbreak happened partly because of those waivers. His position on waivers, should he win in November, will directly affect Florida's outbreak risk.
Sources
- No evidence linking illegal immigration to measles outbreak, despite Byron Donalds' comment
- La inmigración ilegal no causó el brote de sarampión, pese a las declaraciones de Byron Donalds
- Measles Cases and Outbreaks
- South Carolina measles outbreak ends after 997 cases; work continues on lessons learned
- Byron Donalds says illegal immigration drives measles outbreaks. CDC data say otherwise
- U.S. Measles Cases Hit Record-Breaking 35-Year High in 2026
- Measles outbreak linked to Florida university: cases keep rising
- US exceeds 1,900 measles cases as outbreaks expand
- Measles vaccines in Mexico
- U.S. kindergarten vaccine coverage falls, CDC says
- CDC finds childhood vaccine exemptions for personal or religious reasons hit new record
- Kindergarten Routine Vaccination Rates Continue to Decline
- Map Shows Vaccine Rates Among Kindergarteners Compared to Outbreak Hotspots
- Measles surge continues in Americas, with outbreaks in 10 nations
