THESSALONIKI, Greece (AP) — Doctors marched with their families and a few friends in Greece's second-largest city Saturday not to protest, but to debunk misinformation about face masks circulating during the coronavirus pandemic.

A few dozen people fast-walked and ran 2 kilometers (1.25 miles) through central Thessaloniki while wearing face masks and then measured their oxygen and carbon dioxide levels, finding them all normal.

Opponents of mandatory face mask use have spread the claim that wearing face coverings makes people short of breath and actually is bad for their health. Doctors specializing in respiratory medicine wanted to prove them wrong.

“Face masks, alongside social distancing and personal hygiene, are the only measure of protection against the coronavirus,” Dr. Iraklis Titopoulos, a pulmonologist, told The Associated Press after the demonstration in Greece.

“I would never have believed that such a large part of the population would deny the obvious,” he said.

A lot of individuals with chronic lung obstructions are pressing their doctors to write affidavits that would exempt them from wearing masks, Titopoulos said. Others are asking to be excused from going to work.

New coronavirus cases, but not deaths, have surged in Greece since early August, with nearly 80% of the country's more than 19,300 confirmed cases reported since then. With the summer tourism season now over, authorities say people not wearing masks and failing to keep social distancing are to blame for the surge.

Greek Prime Minister Kyriakos Mitsotakis said Saturday that while local lockdowns will be used to keep the coronavirus from spreading, a second nationwide lockdown is “almost inconceivable.” At the same time, he said he expected “a very difficult three to four months” ahead.

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Demetris Nellas reported from Athens, Greece