What Will Happen to the Flu?

It turns out that no one seems to know what will happen to the flu.

Well, we do know one thing.  

“We do not know when it will come back in the United States, but we know it will come back,” said Sonja Olsen, an epidemiologist at the C.D.C.

The question - actually, two questions - seems to be:  what is it that will come back, and will our immune systems be ready for it?

Flu shots are designed in the middle of one flu season, for use in the next year's flu season.  Predicting which flu strains (think "variants") will be active the following winter is a complicated and imperfect process, and is probably the reason that flu vaccines exhibit effectiveness of only 40% - 60%.  In a world where our COVID jabs are well over 90% effective, those numbers don't inspire confidence.  Yet they are the best we have been able to do.  All this occurs in an environment where the population, having been exposed to many flu strains over the years, has developed (individually, very different levels of) immunity to many of the previous years' strains.  Nevertheless, somewhere between 12,000 and 61,000 Americans have died of influenza, each year since 2010, according to the CDC.  You'd think they'd be able to narrow that down - statistics with that range are not particularly useful - but that's where we are now.

And where will we be in the new world?  The interesting thing about the 2020-2021 flu season is that there wasn't one.  Flu cases have been essentially at zero for about a year now.  It's not known whether extensive public health measures (masks, distancing, hand-washing) had a major effect, or whether the coronavirus just muscled the flu out of the environment:

The mere presence of the coronavirus may have also played a role in suppressing flu cases, said Dr. Webby, because there is often just one dominant respiratory virus in a population at a given time. “One tends to keep the other out,” he said.

The two question that will have a great impact on the new world are these:  will the flu's year-plus hiatus reduce its ability to produce the new strains that have the greatest impact, thus making for a very benign flu season or two?  Or will we lose our immunity - and/or lose the ability to develop immunity by being exposed to this year's strains?

“Every year, anywhere between 20 to 30 percent of the population gets its immunity sort of boosted and stimulated by being exposed to the flu virus,” Dr. Webby said. “We are not going to have that this year.”

“Decreases in natural immunity are a concern,” Dr. Olsen said, “and lower immunity could lead to more infections and more severe disease.”

Or both?

It is possible for the new world to be a place where sick people wear masks and keep their distance and wash their hands a lot.  This would have a significant impact on the severity of flu season, and save thousands of lives.  What are the chances?

The last time Americans had a chance to make those behaviors part of the culture, Dr. Baker pointed out, they did not.

“The 1918 influenza pandemic should have been something that gave us some sort of societal learning,” said Dr. Baker, but behavior did not change. “So what is the journey you are about to go on from the Covid-19 pandemic, along that axis?” she added. “Will you wear your mask, even if no one else is?”

There are wide swaths of America (and other countries) which have actively resisted making those behaviors part of the culture this time, as well, even with a death toll in the millions worldwide.

So what will flu season look like in the new world?  It will depend on factors out of our control - the number and severity of new strains, and our immunities after a year of no flu.  It will also - perhaps most significantly - depend on measures completely in our control.  Are we smarter than we were in the 1920s?

Stay tuned.