SAN FRANCISCO (KGO) -- Strong reaction is coming in after a federal judge struck down the mask mandate on airplanes and mass transit.
Faces can now be seen at the airport and on planes -- And the reaction from doctors, is a bold one.
"It sets a really scary precedent for a time when we think about public health emergencies and whether or not judges and politics can override what the CDC is saying," says UCSF's Dr. Peter Chin-Hong.
"Even companies like Delta now calling this an ordinary seasonal virus in a press release and it's not ordinary, and it's definitely not seasonal yet," says ABC's Dr. Alok Patel.
RELATED: Which airlines, airports, transit agencies, ride shares dropped mask mandate after judge's ruling
And while some travelers are choosing to unmask, others still are not.
Tuesday night ABC7 News spoke with researchers who have studied aerosol dispersion and COVID transmission on airplanes.
In 2020, Sean Kinahan and the National Strategic Research Institute at University of Nebraska, was part of a group that found coronavirus transmission was reduced by more than 99 percent on planes due to high air exchange rates, Hepa filtered recirculation, and downward ventilation.
"50 percent of the air is coming in fresh, 50 percent of the air is going through a Hepa filter," said Kinahan.
But Kinahan says the study didn't account for people sneezing or talking to you in close proximity on a plane without a mask on. Research scientist Shanna Ratnesar-Shumate questions the moments getting to that airplane.
"I think my biggest concern with the change in the mask mandate is really the crowded airports," said Dr. Ratnesar-Shumate, who is a research scientist and associate professor in the field.
LIST: Bay Area airports, public transportation still requiring masks
And just as areas across the country have varied in mask use, the same appears to be again happening. Dr. Peter Chin-Hong flew from New York to San Francisco when the mandate was dropped.
"On my San Francisco flight people were very quiet, everyone kept their mask on, no one was dramatic about it," said Chin-Hong.
Ratnesar-Shumate though flew from Washington D.C. to Omaha, Nebraska.
"I just flew today and I was shocked. It was like 80-percent plus people are not wearing a mask right now and the airports are packed.
While BART, MUNI, and VTA are keeping mask requirements in place, AC transit is dropping theirs. It will be voluntary for them starting on Wednesday April 20.