NEW YORK (NYTIMES, REUTERS) - Public health experts reacted with dismay to a federal judge's ruling on Monday (April 18) that struck down a mask requirement for plane, bus and train passengers, expressing concern that the case would set a precedent that erodes the authority of public health agencies and hampers their ability to respond to health emergencies.

The Florida judge's ruling was issued less than a week after the US Centers for Disease Control and Prevention (CDC) had extended its mask order through to May 3. The ruling also came in the middle of a school vacation that coincides with several major religious holidays, when many families are travelling to see relatives, some for the first time in two years.

Many airplane passengers flung their masks off and cheered when pilots made announcements saying that the rule was no longer in effect. Others who have disabilities, are immunocompromised or were travelling with children too young to be vaccinated were caught off-guard and distressed that the rules were changed literally mid-flight.

"If this ruling stands, it could put the American public at great risk," said Dr Richard Besser, president and chief executive of the Robert Wood Johnson Foundation and a former acting director of the CDC.

He added that his concerns were less to do with the immediate consequences for mask mandates than with "the implications for future crises, of the ability to put in place simple public health measures to keep people safe".

Dr Lakshmi Ganapathi, who teaches paediatrics at Harvard Medical School, pointed out that the ruling coincides with a recent rise in Covid-19 cases nationally, driven by a rise in cases on the East Coast.

"I think it's extremely shortsighted and, if I were impolite would say, kind of stupid," Ganapathi said. "This ruling is ill-timed, and it's not commensurate with public health principles."

She noted that low booster rates among seniors and other vulnerable groups, including low-income people who rely heavily on buses and trains for transportation, make them susceptible to infection, and there is still no vaccine for very young children. Banking on immunity from previous infections and vaccinations for protection may be overly optimistic, as emerging new variants could evade immunity, she said.

Moreover, the widespread use of home testing kits, the results of which go unreported, means that official case counts do not reflect the true number of new cases. A rise in hospitalisations is not a reliable or timely indicator of severity either, Ganapathi said, since hospitalisations rise several weeks after cases begin to increase.

"Once hospitalisations start rising, it's baked in - you haven't done anything to stop it," she said. "And a proportion of those hospitalised will die."

The CDC issued an order in January 2021 requiring people to wear masks while using indoor public transportation and when inside transportation hubs, such as airports and bus and train stations.

In a statement released on Tuesday, the agency said that as a result of Monday's court ruling, the order was no longer in effect and would not be enforced, although the agency still recommended masks inside public transportation settings.

Supporters of masks have started an online petition urging major airlines to designate some flights as mask-required in order to give customers a choice.

Even some experts who had previously supported the lifting of the government mask mandate for passengers said they were troubled by the precedent that the federal judge's ruling could set.

Several said they hoped that the Biden administration would challenge the ruling. President Joe Biden said on Tuesday that Americans should decide for themselves whether to wear masks.

The US Justice Department said it would appeal the ruling by District Judge Kathryn Kimball Mizelle that the 14-month-old directive was unlawful, if the CDC determined the mandate was needed to protect public health.

Dr Leana Wen, a public health professor at George Washington University, had strongly criticised Philadelphia's decision to reinstate mask mandates this week. She clarified on Tuesday that she still strongly supported the wearing of high-quality masks like an N95 and that she merely thought a government mandate was not appropriate at this time.

"I don't want people to get the wrong message - I don't want people to think that masks are no longer required or shouldn't be worn," Wen said. "The message is that at a certain point the government can no longer require you to do the right thing."

Dr Robert Wachter, chair of the department of medicine at the University of California, San Francisco, also had said he favoured lifting mask requirements. However, both he and Wen noted that it was critically important for the government to have the authority to issue mandates during public health crises in order to respond to future threats, including new variants of Covid-19.

"If this becomes a precedent, that a judge can overrule government and CDC experts, that puts us in a problematic place for the next surge, the next pandemic, bioterrorism or who knows," Wachter said.

"Government needs to be able to act, and to imply government does not have that authority is deeply concerning."

He noted that he would continued to wear a mask on flights and strongly encouraged his family and loved ones to do so, although he did not think the situation was sufficiently dire to justify a government mandate.

"Should you wear a mask when you're in an aluminium tube, shoulder to shoulder with people for six hours?" Wachter said. "I think you should, and I will."