July 22 (UPI) -- The 2020-21 flu season was the lightest on record since at least 1997, the first year in which cases of the virus were tracked, according to data released Thursday by the Centers for Disease Control and Prevention.
Well under 1% of more than 1.1 million specimens collected from people experiencing flu-like symptoms tested positive for the seasonal virus, the agency said.
In a "typical" flu season, in which an estimated 35 million people are infected with the virus, as many as 25% of specimens tested come back positive, based on historical CDC data.
The reduction in flu cases seen between October 2020 and May 2021 is likely due to measures taken to limit the spread of COVID-19, such as the wearing of masks that cover the nose and mouth and social distancing, the CDC said.
Like COVID-19, the flu is spread through virus droplets emitted from the mouth and nose.
"The same prevention measures we use to prevent COVID-19 disease work for the flu, including physical distancing, masking, avoiding crowds and staying home when sick," public health specialist Brandon Brown told UPI in an email.
"[This is] another reason for everyone to get the flu vaccine ASAP with return to work and return to school, which means a return to exposure," said Brown, an associate professor of social medicine population and public health at the University of California-Riverside.
Similarly, samples testing positive for respiratory syncytial virus, or RSV, which causes the common cold, dropped from 15% in the months leading up to the COVID-19 pandemic in 2020 to between 1% and 2% throughout the rest of the year and into May, the agency reported.
Over the previous four years, rates of positive tests for this virus never fell below 3% and ranged as high as 17%, according to the CDC.
Between April 17 and May 22, the percentage of specimens testing positive for RSV increased from 1.1% to 2.8%.
During this period, many regions across the country relaxed restrictions regarding masking and large gatherings, said Brown, who was not part of the CDC analysis.
Similarly, the percentage of specimens testing positive for respiratory adenoviruses, which can also cause the common cold, as well as pneumonia, ranged from 1.2% to 2.6% between January 2020 and April of this year, before increasing to 3% in May, the CDC said.
In a typical month before the COVID-19 pandemic, this number would be as high as 15%.
It is unclear whether the "historic lows" for these and other respiratory viruses reported by the agency, will continue through the fall and winter, given that COVID-19 restrictions have been relaxed in many parts of the country, according to Brown.
However, the reduced spread of these diseases, which can cause severe illness, particularly in older adults and those with chronic health issues, shows the value of face coverings and other control measures, including vaccination, he said.
"Many countries in the world utilize face-covering as part of their daily lives, and some more specifically if they are going to be in public when they are sick," Brown said.
"Wearing a mask in public when you think you might be getting sick is a show of respect to the health of others, and it is also simple and something that we can all utilize when inside in public spaces or outside with large crowds, to prevent a number of respiratory viruses," he said.