What If Covid-19 Measures Killed Season?

The Covid-19 pandemic fulfills many of the worst expectations that public health experts in the U.S. and Europe have had for fall and winter. One thing they care about, though, doesn’t seem to happen, though: Covid’s destructive “twindemia” and seasonal flu.

Instead, the flu is AWOL – at least so far. In New York, which publishes a convenient daily count of emergency visits for flu and other conditions, numbers less than one-third of the recent standard for the first half of December.

This apparent absence of flu is almost certainly not just a lucky break. Nor is it the result of a cover-up in which authorities calculate flu cases as Covid-19 cases (a seemingly popular theory in some Covid non-racist circles). It is it is conceivable that New York emergency rooms count fewer coronavirus cases as influenza than last March, when Covid tests were scarce and health workers were less familiar with Covid symptoms. It is also possible that people only avoid emergency rooms if they can at all. But results from positive flu tests tracked in FluView by the U.S. Centers for Disease Control and Prevention show an even more dramatic decline.

That dark blue line, which is almost indistinguishable from zero for most of the year, is 2020. The sum of a positive test for the week ending December 5 – the most recent data available – was only 56. In the same week from last year it was 6,435. The onset of influenza season in the northern hemisphere is generally considered to be the 40th week of the year, which ended on October 3, making December 5 the end of the 49th week. Here is a ten-year value of positive tests for the first 10 weeks of flu season:

Yes, the 2011-2012 flu season started with an even lower positive test score. But that’s misleading, as the number of flu tests done has grown a lot since then (although it’s still by no means close to the number of Covid-19 tests done this year). Those 511 positives in the first 10 weeks of the 2011-2012 flu season were out of 40,150 tests, for a positivity of 1.3%. This year’s 602 positives out of 401,112 tests, for a positivity of 0.15%. Anyway so this flu season in the US is on track to be much milder than what turned out to be the deadliest flu season of the past decade and possibly the deadliest flu of the 1980s.

Similar trends can be seen all over the world. “In the temperate zone of the northern hemisphere, influenza activity has remained below seasonal levels,” the World Health Organization summarized in its most recent weekly influenza update. That is, there is less impact of flu now, in late fall, than usual in summer. The WHO and other public health agencies have of course hesitated to declare victory against the flu yet – it’s still early in the season, and there’s another disease that is wreaking havoc even if the flu isn’t. The head of the manufacturer of smart thermometers Kinsa Inc. is less restrained, telling the New York Times that “It looks like the twindemic isn’t going to happen.” And it’s clear from 2020 flu seasons that are already over that something extraordinary is happening.

Studies have found that in the US and Europe the flu effect has fallen much more sharply than usual in late winter and early spring this year. And in Australia, where peak flu season generally lasts from April to September and Covid control efforts have been much more successful than in the US or Europe, there has been no flu season at all.

Since the beginning of May (the last full month of autumn in the southern hemisphere), five flu tests have returned positive in Australia, according to the WHO’s FluNet database. Since mid-July, no one has. Other countries in the temperate zones of the southern hemisphere have had similar experiences.

Why is this happening? The push for more people to get vaccinated against the flu this fall to avoid the dreaded twememia may have had some effect, but that doesn’t explain why the flu effect fell last spring. The obvious explanation is simply that the things that individuals and governments have done to slow the spread of Covid-19 have caused the spread of influenza, a respiratory disease that is transmitted similarly, if not identically, to a screaming stop.

These remedies are probably more effective against the flu than against Covid, as the flu is much less contagious than Covid. A rough measure of contagion is the basic reproductive number – the number of people each person with the disease can expect if everyone behaves normally. For seasonal flu it is 1.3, in flu pandemics it was higher than that, but still below 2. For Covid-19 it is probably somewhere between 2 and 4.

Disguise, working at home, banning large gatherings and other social distancing means – along with more people gaining immunity by contracting Covid-19 – seem to have brought Covid’s effective breeding number in the United States to no more than 1. (When last I checked the estimates on rt.live, Tennessee had the highest rate at 1.22 and Wyoming the lowest at 0.85.) In all respects, this also pushed the effective breeding number for the flu much less than 1.

One lesson from this is that the oft-heard lament that the United States and many European countries have failed to fight the pandemic is wrong. Certainly, a quick glance at East Asia clearly shows that the West could do much, much better. But considering how successful we have been in stopping the flu, it seems clear that we have also managed to slow down Covid. The recurrence of the disease this fall has been bad, but it could be much, much worse.

Another lesson is that “non-pharmaceutical interventions,” the expression of art for all the things we’ve done to curb the spread of Covid while waiting for vaccines, should be a bigger part of the gear to fight the flu. That doesn’t mean we close all borders and restaurants every winter, but less expensive resources like seriously washing hands, wearing a mask when you’re not feeling well, working from home if you were exposed and keeping sick visitors and workers away from nursing homes could save thousands lives every year. And if a new pandemic flu appears, that’s as deadly as, say, the 1918 variety (which was much more deadly than Covid-19, especially for young people), more costly interventions would almost certainly be worth the price.

The wait for a pandemic flu vaccine would be shorter than it was for Covid-19. It took about six months of identifying a new strain of H1N1 flu in 2009 until a vaccine became widely available. In a presentation last week at a conference of the European Scientific Working Group on Influenza, professor of vaccinology Florian Krammer of the Icahn Medical School at Mount Sinai in New York said that with the right preparations the wait could be shortened to three months. If mask mandates, social distancing, and other non-pharmaceutical interventions can stop flu, and it should be stopped for only three months, it would be crazy not to use them.

This section does not necessarily reflect the opinion of the editorial staff or Bloomberg LP and its owners.

Justin Fox is a columnist on Bloomberg Opinion on Negotiation. He was the editorial director of Harvard Business Review and wrote for Time, Fortune and American Banker. He is the author of “The Myth of the Rational Market.”