The highest estimate of illegal aliens living in the US that I've seen is 15.8 million. I haven't seen data on how many times this population leaves and returns to the US in a year, but I would think that given the difficulty and risks associated with crossing the border without authorization, the frequency would be fairly low. Certainly less than once per year per person. Probably even much lower than that. https://www.migrationpolicy.org/commentary/us-unauthorized-immigrant-population-new-peak In contrast, US citizens made 109 million overseas trips in 2025. Even after taking out the 14 million trips to Canada, the total would still be a multiple of the number of entries by illegals in the course of a year. Roughly 40 million US citizens visited Mexico and another five million visited other countries in Latin America, countries where the vast majority of illegal aliens come from. Then there are the others who visited Asia, Africa, and elsewhere where measles is endemic. https://tourismanalytics.com/usoutbound.html But sure, measles is primarily brought into the US by illegals, right? /s
