It is unprecedented in recent flu seasons and mirrors national trends — the Centers for Disease Control and Prevention say flu activity has been “usually low” this season. Cases in Pennsylvania are down so much the health department won’t release a county-by-county breakdown of cases because to do so risks identifying flu patients.
Statewide there have been 3,351 lab-confirmed flu cases and 18 flu-associated deaths as of April 10, according to the weekly flu activity report released Tuesday by the health department. When a positive lab test is reported to the state, it’s logged as a confirmed flu case. The flu’s been detected in all 67 counties, resulting in 43 flu-related hospitalizations this flu season.
Pediatric deaths are generally considered an indicator of a flu season’s severity, which this year officially began Sept. 27 and ends May 22. There were 198 pediatric deaths nationwide last flu season. This year, there’s been one, according to the CDC.
Illness tends to peak in the middle of the winter, often on the heels of the holidays, but there was no sustained peak this year, just one jump the week of Nov. 30.
And this is despite a reported sixfold increase in flu testing at public health labs nationally, most of which checked for Influenza A and B when testing for COVID-19.
“It is important to say flu is still tested for and if flu were occurring we would know about it and when flu starts to emerge again we’ll know about it,” Lehigh Valley Health Network infectious disease specialist Dr. Luther Rhodes said.
The CDC recommends that providers test patients with coronavirus symptoms for both COVID-19 and the flu, because it is impossible to differentiate between the two without testing and patients can have both at the same time, explained Amber Liggett, a health department spokesperson.
“Since flu and COVID-19 are both respiratory illnesses and are spread the same way, there have been fewer cases of flu this year since there’s been more mask-wearing, social distancing and sanitation. Other factors that could have participated in having a mild season include better flu vaccination coverage, efficient seasonal flu vaccine, mild flu strains such as the strains that caused mild flu seasons previously, and viral competition, in which the pandemic virus has the advantage,” Liggett said. “It is likely that the mild flu season is the result of some or all of the mentioned factors.”
Over this flu season, the coronavirus has infected 933,432 Pennsylvanians and claimed the lives of 17,417 people.
Rhodes said the health network began to see a dramatic drop in flu cases in February 2020 when the coronavirus began spreading in the community despite widespread flu testing. Coming into the 2020-21 flu season, there was widespread concern we could see twin pandemics that crushed U.S. hospital systems.
But this flu season never gained steam. It hasn’t 100% disappeared, but it’s close to it, Rhodes said.
“The COVID precautions alone don’t explain it,” he said.
If the precipitous drop of flu cases was a result of just masking and social distancing, we’d see pockets of flu outbreaks in places with less compliance with mitigation measures, but that is not happening, he explained.
“I think the pandemic has impacted the behavior of the influenza virus,” Rhodes said.
Cases are unusually low nationwide in a remarkable way, he said. Some of this is likely related to natural competition between the flu and the coronavirus and COVID is winning currently. There also may be higher flu vaccination rates and the vaccine itself may be a better match to the dominant strain.
“The flu virus circulates widely in nature, so human behavior alone is not going to alter influenza. It hasn’t to date,” Rhodes said. “It can make things worse by being careless. We aren’t going to mask it out of existence. We aren’t going to hand wash it out of existence. Flu has the ability to carve out its own path, it is not just what people do. It has a lot to do with its spread in nature, in birds and pigs. Some of our worst human flu strains are shared with pigs and birds.”
The health network internally monitors all of the flu testing across its hospitals and doctor offices, so Rhodes has a clear snapshot of the flu’s spread in the Lehigh Valley at any time. The vast majority of rapid testing in doctor’s offices is not reflected in state flu case reporting, he noted.
The first week of this flu season there were 142 cases reported in the network compared to 518 the year prior. On Feb. 19 of this year, there were 72 flu cases compared to 927 in 2020.
“It is dramatically reduced,” Rhodes said. “Other respiratory viruses have dramatically decreased in number too.”
There are two types of flu: A and B. In most seasons, Flu A predominates at the start and then Flu B near the end, Liggett of the health department, noted. Some seasons, H1N1 (a Flu A subtype) dominates in the beginning and then H3N2 (another Flu A subtype) takes over. The latter is known to cause more complications and deaths and seasonal vaccines are less effective against it, she said. Flu B is always milder and vaccines have a higher efficacy against it.
“The circulating strains of flu may affect the activity,” Liggett said.
The health department continues to monitor what the rest of the flu season may bring, Liggett said.
“Flu is unpredictable and its activity depends on many factors, including consistency in using COVID-19 mitigation actions (e.g. face masks, social distancing, hand hygiene, vaccination, etc.),” she said.
Rhodes cautioned no one should think this means we’ve beat the flu.
“What happens with the flu as time goes on? There is a lot of speculation about a virus suppressed in nature for whatever reason, natural selection, second virus elbowing it out, can emerge with an attitude and rush back,” Rhodes said, noting he’s prepared for when cases start popping up again.
COVID mitigation measures and changing human behavior have played a large role, but that’s not the entire story and society won’t support such precautions long-term, Rhodes said. We’ll have to strike a balance, like wearing masks early in flu season, and rethink our approach to flu vaccines, he said.
Rhodes is hopeful with the rise of mRNA vaccines, like the Pfizer-BioNTech and Moderna COVID-19 shots, becoming more mainstream, science tries to modernize the flu vaccine. If a flu vaccine is 40% effective against the dominant flu strains that’s considered a success, he said. The Pfizer and Moderna vaccines boast efficacy rates of 90% or better.
“I have been saying for a long time that our wold’s flu vaccine is not up to par,” he said. “The egg and yolk technology is horse and buggy. …We need to up our game to get the flu vaccine to a much better outcome. “
Rhodes is hopeful a better flu vaccine can be one positive outcome of the coronavirus pandemic
The vast majority of people who contract the flu never get tested or go to the doctor, so typically case counts actually only represent a faction of the flu in the state at any time. In a normal flu season, it is estimated that 5% to 20% of Pennsylvanians, or 600,000 to 2.4 million people, get the flu each year and 120 to 2,000 die from flu-related complications.
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