The U.S. Department of Homeland Security is now requiring non-U.S. essential workers who cross borders for work to be fully vaccinated against COVID-19. This would include workers like truck drivers and nurses. Starting Saturday, any non-U.S. individuals will have to show proof of vaccination at land ports and ferry terminals.
See "Essential workers crossing boarders must be vaccinated, DHS says", David Shepardson, Reuters, January 21, 2022