What happened to the flu? Here’s why influenza spread is way down this season
Deadly coronavirus pandemic aside, the U.S. would normally be seeing loads of flu cases this time of year.
But health care professionals aren’t seeing their standard influenza-ridden patients this season, suggesting the virus isn’t making its usual rounds in the northern hemisphere.
“We are testing thousands of people in our emergency room settings and in our hospitals for a combination of COVID and flu, and we’re essentially seeing no flu,” Dr. Randy Bergen, a flu expert with health care company Kaiser Permanente, told ABC7. “Some weeks we’ll have no cases, others we’ll have maybe one or two.”
Health officials in the southern hemisphere — including Australia and South America, where the seasons are reversed — said their flu season was virtually nonexistent while coronavirus cases were spreading like wildfire.
The Centers for Disease Control and Prevention says national flu activity “remains lower than usual,” including flu-related hospitalizations, but there’s still time for it to increase in the coming months.
Since Sept. 27, there have been a little over 1,000 influenza cases reported in the U.S., the latest CDC data shows, but an agency spokesperson told McClatchy News in an email that reported clinical and public health positive flu cases aren’t “necessarily an accurate number.”
That’s because “flu illness is not a reportable disease and not everyone who gets sick with flu seeks medical care or gets tested,” the spokesperson said.
The agency usually provides estimates on the number of illnesses, doctor’s visits, hospitalizations and deaths associated with the flu, “but because there isn’t much activity, we haven’t been able to generate [them],” they added.
For comparison, the CDC estimated that there were 38 million flu cases, 405,000 flu hospitalizations and 22,000 flu deaths during the 2019-2020 season, which began in the fall and ended in spring.
Meanwhile, infectious diseases experts say it’s hard to pinpoint why so few people are catching the flu amid a pandemic involving a similar respiratory virus.
They speculate that flu vaccinations, coronavirus priority in health care systems, competition between viruses and COVID-19 preventive measures such as mask wearing and social distancing all play a role in the abnormally inactive 2020-2021 flu season.
We can prevent the flu better than COVID-19
The coronavirus appears to spread more easily than the flu because it typically takes more time before people show COVID-19 symptoms — if they show them at all — which makes them contagious for longer, according to the CDC.
The flu is more preventable than COVID-19, as well, thanks to annual vaccines designed to target whatever version of the influenza virus that’s spreading in a given year.
About 189 million flu vaccinations were given in the U.S. as of Dec. 4, a CDC report says. That’s the highest number of flu doses distributed to Americans during a single influenza season.
It can help explain why there are so few flu cases so far, experts say.
“Either virus can make you very sick or lead to death, but with influenza we have the opportunity to focus on prevention because we have additional tools in our arsenal that help decrease overall infections,” Dr. Allison Bartlett, an infectious diseases expert with UChicago Medicine, wrote..
COVID-19 prevention strategies may also prevent flu spread
Health experts say preventive measures for COVID-19 — such as mask wearing, social distancing, working from home and closing schools — might be making a dent in the spread of other respiratory illnesses, such as the flu.
The CDC says children in school usually play large roles in spreading influenza, but “the effectiveness of school closures alone is not clear because adults have other exposures.”
There is evidence, however, that supports the use of masks by infected people to reduce the spread of any respiratory virus in the health care setting, in homes and in the general community, the CDC says.
Researchers in Taiwan compared 25 weeks of data on the flu, Streptococcus pneumoniae disease and pneumonia deaths from 2016 to 2020 and found that all three illnesses spread less in 2020 than the same weeks in the previous years.
The downward trend was particularly apparent when the country enforced COVID-19 preventive measures, the study found.
A separate paper from Japan came to similar conclusions after discovering that flu activity was lower week-by-week in 2020 compared to the last five years. The researchers said “awareness regarding measures to reduce the risk of [COVID-19] transmission,” could have affected the spread of influenza.
Border closures blocking international travel to reduce the spread of COVID-19 have also likely helped prevent the spread of the flu, experts say.
Flu patients may not be visiting hospitals, getting tested
After the COVID-19 pandemic was declared a national emergency on March 1, the nation’s influenza activity “declined sharply within two weeks... although the exact timing varied by location,” the CDC report says.
Dr. Brendan Flannery, co-author of a letter calling for organized testing for both influenza and COVID-19, said the worst-case scenario is that people suspected of having the flu have been staying home, not getting tested and avoiding seeking care because medical centers have been overwhelmed with coronavirus patients.
That could explain why the number of patient samples submitted for flu testing dropped by 61%, while the number of positive test results plunged by 98% following the nation’s first lockdowns, according to the CDC.
Competition between coronavirus and influenza?
Experts say there’s no biological reason why someone can’t be infected with both coronavirus and influenza, however it’s unknown if having had COVID-19 makes you less likely to get the flu, or vice versa.
“Unfortunately, there is no antibody level cross protection from flu and COVID-19. Your ability to fight off one is independent of the other,” Bartlett of UChicago said.
But there is the possibility that coronavirus and influenza are battling to win over hosts, given they both attack the respiratory system.
“Now whether it’s immunity or they just suppress the growth of another virus, it’s not really clear, but there’s certainly an inkling from a couple of years ago, that viruses can compete,” Dr. Yvonne Maldonado, a pediatric infectious diseases expert at the Stanford University School of Medicine, told ABC7.
The CDC report also mentions “viral interference.”
“Viral interference might help explain the lack of influenza during a pandemic caused by another respiratory virus that might outcompete influenza in the respiratory tract,” the reports reads. “This possibility is less likely in the U.S. because influenza activity was already decreasing before [coronavirus] community transmission was widespread in most parts of the nation.”
This story was originally published January 6, 2021 at 10:29 AM with the headline "What happened to the flu? Here’s why influenza spread is way down this season."
