People who are fully vaccinated no longer have to wear masks in outdoor transportation settings, including at airports, train stations, ferry docks and on vehicles with outdoor spaces, according to updated guidance from the Centers for Disease Control and Prevention.

“CDC has removed the requirement to wear a mask in outdoor areas of conveyances and transportation hubs because of the lower risk of transmission outdoors,” the agency said in a notice posted Thursday.

The update is part of an effort by federal health officials to more closely align recommendations for those have been fully vaccinated. In dropping the requirement for mask-wearing when outdoors, the CDC cited research showing there is a low risk of virus transmission in those settings.

However, the CDC emphasized that all individuals, regardless of vaccination status, must continue to wear masks when indoors and on all modes of transportation into, within or out of the United States. That includes in airports, on airplanes, in subway cars and on trains. The CDC also recommends that those who have not been fully vaccinated wear masks while outdoors to “protect themselves and others who are not fully vaccinated.”

Children under 2 and those with certain disabilities are exempt from the mask requirement, but others could face penalties if they refuse to comply, including being barred from boarding. The Transportation Security Administration, which has been charged with enforcing the mandate in transportation settings, recently extended the mask requirement through Sept. 13.

For those who fail to comply, penalties begin at $250 and increase to $1,500 for repeat offenders.

President Biden issued a federal mask mandate for transportation on his first full day in office. The CDC later issued an order that required all people to wear masks at travel hubs and when traveling on public transportation.

Even so, some have refused. The Federal Aviation Administration said that of the 2,500 reports of unruly passenger behavior it received through the end of May, 1,900 involved passengers who refused to follow the federal mask mandate when flying.