Last year's influenza season turned out to be the mildest on record, but health experts have renewed warnings that a 'twindemic' - in which flu and COVID-19 cases simultaneously rise and overwhelm hospitals - may be possible this year, and they urge Americans to get their flu shot.
The Centers for Disease Control and Prevention reported 1,675 cases of influenza from Sept. 28 to May 22, representing only .2% of specimens tested. But it's difficult to predict what this year will look like, health experts say.
They worry it may resemble a more typical flu season, as students get back to in-person learning and states loosen mask and social distancing mandates amid a return to social gatherings.
That is especially concerning as COVID-19 cases driven by the highly contagious delta variant rise throughout the country. A USA TODAY analysis of Johns Hopkins data suggests the U.S. reported more than 1.05 million cases in the week that ended Monday, amounting to 104 cases every minute.
Severe illness and deaths are also rising, filling ICU beds and threatening hospital capacity. The country recorded more than 7,200 COVID-19 deaths in the week that ended Monday, the equivalent of a Pearl Harbor attack three times a week, or a 9/11 attack every three days.
"We were worried about the 'twindemic' last year and we face the same threat this year," said Dr. Daniel Solomon, a physician in the division of infectious diseases at Brigham and Women's Hospital. "COVID-19 is likely to continue, and we face the threat of dual respiratory viruses that could put a strain on our health care system."
Flu shots are now available at CVS and Walgreens, the country's two largest retail pharmacies, and offer co-administration of the COVID-19 and influenza vaccines. The CDC reversed previous guidance to wait at least 14 days between the COVID-19 vaccine and other vaccines, saying "you can get a COVID-19 vaccine and other vaccines at the same visit."
Physicians haven't yet seen any flu cases, but they are seeing an increase in other respiratory viruses that show conditions may be primed for fall and winter flu transmission.
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Respiratory syncytial virus is a common virus that usually causes mild, coldlike symptoms primarily in children, according to the CDC. It's the most common cause of pneumonia in children younger than 1 in the U.S.
"Some of the cases of children that are being hospitalized with COVID also have a co-infection of RSV," said Dr. Jeff Fischer, president at Longhorn Vaccines & Diagnostics, a privately held biotechnology company. "So one of the other concerns is that you see co-infections (of flu)."
RSV in the summer doesn't necessarily predict flu transmission in the fall and winter, Solomon said, but it shows children, who are efficient transmitters of flu, are interacting more in social settings.
In addition to getting the flu vaccine, health experts say it's important to practice some of the health measures from the pandemic that last year prevented flu transmission.
A nationwide lockdown is not necessary, they say. They say wearing masks, practicing good hand hygiene and staying home from work when sick are sufficient to keep people from getting sick and infecting other vulnerable populations.
"Last year, we didn't have a very big flu season because people were using masks and that decreased the flu season activity," said Dr. Ricardo Correa, endocrinologist and associate professor of medicine at the University of Arizona College of Medicine. "If we do the same thing this year and we wear masks as much as we can, then the flu season will not hit us as hard as years prior."
Solomon advises people to get their shot around October so protection will last throughout the entire flu season. But if for some reason they don't have the flexibility to wait until then, he urges them to get vaccinated sooner rather than later. A typical flu season in the U.S. peaks between December and February and can last as late as May, according to the CDC.
It's almost impossible to know whether someone has COVID-19 or the flu from symptoms alone, Solomon said. He urges everyone in this position to get diagnostic testing so they can receive the appropriate treatment early and avoid hospitalization
"We do face this threat of multiple serious respiratory viruses circulating in our community simultaneously," he said. "If that comes to pass, it could strain our hospital system in ways we're seeing now with COVID alone."
Contributing: Mike Stucka, USA TODAY. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.
Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.
This article originally appeared on USA TODAY: Flu shot at Walgreens, CVS: Experts warn of twindemic, urge vaccine