The U.S. is extending a vaccine rule for international travelers at its land borders.

International travelers arriving at land ports of entry or ferry terminals in the United States must continue to show proof of full vaccination against the coronavirus, the Department of Homeland Security said Thursday.

Unlike air travelers entering the United States, land and ferry travelers will still not have to show a recent negative coronavirus test to cross the border.

Homeland Security said that the rules for land and ferry entry were extended after discussions with the Centers for Disease Control and Prevention and several other federal agencies.

International travelers must present a vaccination record issued by a government health agency, along with their passport and other documents, to Customs and Border Protection officers.

The C.D.C. considers people fully vaccinated once two weeks have passed since they received a second dose of the Pfizer-BioNTech or Moderna vaccines or a single dose of the Johnson & Johnson vaccine. Those who have received a full course of other vaccines listed for emergency use by the World Health Organization would also be considered fully vaccinated, the C.D.C. says.

Trade and travel are “essential to our economic security,” Alejandro N. Mayorkas, the secretary of Homeland Security, said in a statement, adding that the administration believes that it can protect public health at the same time.

In November, the Biden administration lifted travel restrictions at the land borders with Canada and Mexico for fully vaccinated travelers, reopening the U.S. to tourists and to people separated from their families during the pandemic.

Commercial drivers and students were among those who were never barred from crossing the land borders, but in January the United States started requiring them to show proof of vaccination when crossing.

Air travelers ages 2 and older generally must show a negative coronavirus test taken the day before boarding a flight to the United States, regardless of their vaccination status or citizenship. Alternatively, people who have tested positive in the past 90 days may travel despite a positive result on a recent test, if they have a signed letter from a licensed health care provider or a public health official saying that they have been cleared for travel.