As Pennsylvanians hunkered down last fall and winter to protect themselves from COVID-19, they experienced a positive side effect: an unusually mild flu season.

The state had only 3,664 laboratory-confirmed flu cases during the 2020-2021 flu season, which officially ended May 22. By contrast, the previous season was particularly bad, with 130,900 cases, the state health department said.

At a press conference Friday, Ray Barishansky, deputy secretary of health preparedness and community protection, said that flu was identified in all 67 Pennsylvania counties, but a third of them had fewer than 10 cases. There were 45 hospitalizations and 21 deaths associated with the flu.

He said the drop in flu cases occurred at a time when testing for flu at public health labs across the nation was six times higher than usual. The state and the U.S. Centers for Disease Control and Prevention recommended that sick people be tested for both flu and COVID-19 because the symptoms alone are indistinguishable.

Flu symptoms include fever, headache, fatigue, dry cough, sore throat, nasal congestion, and body aches.

While he did not have numbers for Pennsylvania, Barishansky said the CDC has reported that a record number of people — 193.8 million — were vaccinated for the flu last year. The previous record was set in the 2019-20 season, with 175 million doses.

» READ MORE: It was an illness-free year for many. Here's what that means for our immune systems.

While flu cases usually drop markedly during the summer, Barishansky said the state continues to monitor for the respiratory virus. He urged anyone with symptoms to seek medical attention and keep their distance from others. Asked if the department would consider mandating masking during flu season, he declined to answer, but added that the pandemic has shown the effectiveness of masks and other prevention measures for protecting others. “We all learned that we have a stake in the general public health, and our actions affect the public health,” he said.