People who are fully vaccinated against COVID-19 can travel within the US without getting tested for the disease or quarantining, health authorities say in new guidance.
The Centres for Disease Control and Prevention had previously cautioned against unnecessary travel even for vaccinated people but updated its guidance on Friday.
"Every day you get more data, and you change your guidance based on the existing data," said Dr Ali Khan, dean of the University of Nebraska's College of Public Health.
Khan said the update reinforces the safety and effectiveness of the vaccines, and is another incentive for people to get vaccinated.
According to the CDC, nearly 100 million people in the US, or about 30 per cent of the population, have received at least one dose of a COVID-19 vaccine.
A person is considered fully vaccinated two weeks after receiving the last required dose.
The guidance should be a shot in the arm for a US travel industry still struggling since the COVID-19 crisis began in early 2020.
Unvaccinated people are still advised to avoid unnecessary travel.
For international travel, the CDC says vaccinated people do not need to get a COVID-19 test before leaving, although some destinations may require it.
The agency says vaccinated people should still get a negative COVID-19 test before boarding a flight to the US and be tested three to five days after returning. They do not need to quarantine.
The US began its vaccine rollout in mid-December.
The first vaccines - from Pfizer and Moderna - require two doses taken a few weeks apart. A one-shot vaccine by Johnson & Johnson was given the green light by regulators at the end of February.