Unvaccinated people who are not American citizens will not be permitted to enter the United States.

What about people coming from Canada and Mexico? If travelers go through the land border, do they have to be vaccinated?

Regardless of whether people fly or drive in from Canada or Mexico they must be vaccinated. Initially, the new policy for international visitors only applied to people boarding an airplane. And vaccination status aside, land borders with Canada and Mexico are currently closed for all but essential travel. But in November, when the United States reopens the land borders, similar restrictions regarding vaccination status will apply, the White House said on Tuesday.

The shift in policy will also eventually affect people who were never banned from traveling across the land border. Commercial drivers and students, for example, will need to show proof of vaccination, starting in January, giving them some time to adjust to the new rules, officials said.

Until November, only essential visitors can drive in. The definition of “essential” offered by the U.S. Embassy and Consulates in Canada includes “work and study, critical infrastructure support, economic services and supply chains, health, immediate medical care, and safety and security.”

What does fully vaccinated mean? Which vaccines will be accepted?

The United States will accept vaccines authorized by U.S. regulators or listed for emergency use by the World Health Organization, according to the C.D.C. This includes Moderna, Johnson & Johnson, Pfizer-BioNTech, two versions of the Oxford-AstraZeneca vaccine, Sinopharm and Sinovac. Russia’s Sputnik V vaccine is not currently on the accepted list, meaning that most Russians and others inoculated with Sputnik V may be prohibited from entering the United States.

People are considered fully vaccinated two weeks after their second dose of a Pfizer or Moderna vaccine, or two weeks after a single-dose vaccine, such as the Johnson & Johnson vaccine, a spokeswoman for the C.D.C. said. “Mix and match” vaccines, an inoculation strategy involving a first dose of one vaccine and a second dose of a different vaccine, will be accepted as long as each dose involved is an accepted vaccine, the C.D.C. said.

How do the new rules affect people from countries that were not on the banned list?

The new policy applies to everyone who is not a U.S. citizen, including individuals from Japan, Singapore, Mexico and many other countries whose citizens have been able to fly to the United States throughout the pandemic. Though vaccination status does not currently affect whether or not these individuals can enter the United States, in November only fully vaccinated travelers will be permitted.

Already these individuals have to show proof of a negative coronavirus test taken within three days of boarding a flight. This requirement will remain.