Dr. Jennifer Caudle urges everyone to get their flu shot before the season is over.
Doctors prepare to fight flu season and Covid-19 at same time
01:45 - Source: CNN

Editor’s Note: Kent Sepkowitz is a CNN medical analyst and a physician and infection control expert at Memorial Sloan Kettering Cancer Center in New York. The views expressed in this commentary are his own. View more opinion at CNN.

CNN  — 

Late last summer, many experts expressed concern that the illness and chaos caused by the Covid-19 pandemic might soon worsen as we entered flu season. Dubbed the “twindemic,” pessimists foresaw a nightmarish overlap of the two viral diseases that could overwhelm the country and the world.

Dr. Kent Sepkowitz

In another corner were the optimists, usually a very small group in public health circles. They suggested that – perhaps – a public motivated to avoid coronavirus by masking, distancing, handwashing and all the rest would actually achieve better control of influenza, a two-for-one sort of bargain.

Thus far, the optimists have won – at least partly. We are seeing historically low rates of flu in the US and the rest of the world right now despite being knee-deep into flu season. Or, in the crisp administrative language of the US Centers for Disease Control and Prevention (CDC), “Seasonal influenza activity in the United States remains lower than usual for this time of year.” (For a quick visual, check the small red triangles in the Figure on Page 5 of the weekly NYC Influenza Report

But the other half of the putative two-for-one bargain has not come through. While our mask and distancing measures largely seem to have stopped influenza (and colds and other winter-time sniffles) in their tracks, the same measures have slowed transmission but failed to stop the spread of Covid-19.

This unanticipated split is very difficult to explain. Understanding it, however, will be crucial to our future efforts to prepare for whatever is ahead, be it Covid-22 or Covid-23 or a novel influenza – or something else even more unexpected.

The plausible explanations for the divergence sort out along two lines: first, maybe the transmission dynamics of the two viruses really are that different; and second, maybe the population’s immune “experience” with these two viruses is wildly dissimilar.

Before working through the possible reasons, it is important to remember that nothing is more predictable in public health than the lousiness of predictions.

It’s possible that the 2020-1 flu season is not minimal but rather that people with symptoms are avoiding the doctor’s office or hospital ERs to avoid potential Covid-19 exposures. Or perhaps flu season is running late. Flu usually has two waves: in December and January, influenza A predominates then gives way, in February and March, to a surge of milder influenza B cases. Maybe we will see a sudden burst of influenza as the winter wears on. But probably not. Other areas, including Asia and the Southern Hemisphere, which has an inverse flu seasonality compared to the US, have found the decrease to be durable.

The transmission dynamics of the two viruses have been studied extensively – at least as well as transmission dynamics can be studied. The tools looking for the key factors are a not-quite-convincing mix of statistical models, cool infra-red videos of people talking, coughing and sneezing, and post-event analysis of bad outbreaks and should-have-been outbreaks. Though elegant, this has the limitations of weather forecasting, however clever the approach.

Plus, all of these attempts to understand things have recently been upstaged by a new perspective: whole genome sequencing of viral strains. Using this approach, we have learned that some strains spread more readily than others. Indeed, studies have demonstrated that the Covid-19 B-117 variant (and others) are up to 50% more contagious than the initial Spring 2020 virus. Understanding spike proteins and attachment to cells may prove as important as determining how long a droplet or aerosol lingers in the air.

The virus is only half of the story in any infection; the other half is the human immune system. A substantial part of the difference in controlling the two viruses may derive from a simple fact: our immune systems have dealt with flu every year for decades, whereas this strain of coronavirus is altogether new to our lymphocytes and other components of our immune response.

That said, there is some accumulating evidence that our immune system is not as Covid-naïve as initially feared. Previous infection with older legacy strains (not Covid-19 in any of its genetically sequenced incarnations such as the B-117 variant) may in fact be beneficial. Recently, researchers showed that infection within the previous five years by old-school mild, sniffle-causing coronavirus was associated with a dramatic reduction in need for intensive and ventilator care after Covid-19.

Immune memory can be quite amazing – which may be good news for those fearful of viral mutations soon circumventing our current generation of Covid-19 vaccines. During the 2009 H1N1 novel influenza pandemic, researchers noted that older patients had less severe disease. A lead theory was that those old enough to have been vaccinated against swine flu in 1976 likely had a superior immune response, despite the 33-year interval.

Maybe, then, some substantial part of the difference in how well masking-distancing-handwashing seems to protect us lies not with differences in the two viruses but rather an individual’s long-memoried immune repertoire.

Getting ourselves ready for the next novel corona or other virus therefore will require much more than the already-Herculean task of understanding everything on earth about the virus itself. Understanding a virus is easy compared to exploration of differences in immunity. The human immune response is composed of many intersecting processes and the whole is much greater than the simple sum of component parts.

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    The all-out scientific assault to fully understand the villain – Covid-19 – seems logical and makes for good, scary headlines. Right now, the path to total panic is ever-near each time something new and frightening is found lurking in the viral genome. That’s a standard reaction to all fresh scientific observations until they settle into their proper context. But we should not give over to the temptation to engage in a dizzying “you think that’s bad, well listen to this” competition with each new insight.

    To remain even-keeled for what’s ahead, we should have a bit more faith in the dexterity of our own immune system. After all, it has gotten us out of our caveman existence, past various plagues, and into the 21st century in one piece. So too should a combination of vaccination and previous infection, along with social distancing and mask wearing, continue to carry us forward – however bumpy the ride.