The Influenza of 1918 and the Coronavirus of 2020: Some Parallels and Differences

Sometime prior to late January 1918, a virus jumped species from birds to humans, probably after passing through another mammal. It spawned a lethal pandemic.

Sometime prior to late December 2019, a virus jumped species from bats to humans, probably after passing through another mammal. It spawned a lethal pandemic.

The parallels between the two viruses and the diseases they caused, H1N1 and influenza and SARS-COV2 and Covid-19 (short for Coronavirus 2019), are significant, but so are the differences.

Both viruses transmit exactly the same way, chiefly through virus expelled when shouting, talking, or for that matter breathing, either in droplets, which fall to the ground fairly quickly, or smaller and lighter aerosolized packets of virus, which can float in the air for hours like dust motes. Both viruses primarily attack the respiratory system; they can bind to cells in the upper respiratory tract, which make them highly transmissible, as well as to cells deep in the lung, which can make them lethal—victims will then in effect start out with viral pneumonia. Though both viruses attack the respiratory system, both can kill through cardiovascular events (in fact all influenza viruses are linked to cardiovascular complications). In addition, both the 1918 influenza virus—but not the other influenza viruses that plague humans—and SARS COV-2 can infect virtually every organ in the body and have particularly pronounced neurological impacts. With both viruses, illness can linger for extended periods, and the 1918 virus also caused some sequelae which did not even surface for several years. Clearly, at this writing it is far too soon to know how long-lasting Covid-19 damage can be and what complications will eventually develop. Some complications of the 1918 virus didn’t surface until the 1920s. Today tests of people, including very young people, who never develop any Covid-19 symptoms show heart and lung damage. Will they suffer serious heart or lung disease in the future? We don’t know.

The viruses also have important differences. Of course they differ in molecular biology, the mechanism by which they bind to cells, and so on, but they also differ in four very important ways which one does not need a microscope to observe.

First, the 1918 virus was much more lethal and much more virulent. It killed between fifty and 100 million people; adjusted for population that would equal somewhere between 220 million and 440 million people today. The direst, worst-case projections for Covid-19 do not call for anything like those numbers. The case mortality of 1918’s H1N1 in the West was probably two percent to two and a half percent, but it was much higher in the developing world, probably six percent to eight percent, most likely because people outside the West had seen few if any influenza viruses and had little or no cross-protection from prior exposure.

Second, H1N1 killed otherwise healthy young adults in large numbers, with well over ninety percent of the excess mortality in people younger than sixty-five and the peak age for death in the late twenties. (Other influenza pandemics also lowered the average age of the dead; the 1957 and 1968 pandemics saw only a slight downward trend, but 2009’s H1N1 outbreak, although generally mild, had a strikingly similar age pattern to 1918 in those it did kill, with the peak age for death being thirty-one). Children also died; in 1918 children aged one to four died in numbers equal to today’s all-cause mortality—the combined deaths from all drownings, accidents, cancer, heart disease, infections, murder, etc.—over a period of twenty-three years and children aged five to nine did not fare much better. Covid-19 of course does the opposite. Children die very, very rarely, and the overwhelming majority of deaths occur in people older than sixty-five.

Third, in influenza those who never develop symptoms at all do not infect others; pre-symptomatic transmission does occur, but only during a relatively brief period. With SARS COV-2 pre-symptomatic transmission occurs probably for about two days, and symptomatic people generally can transmit disease for another ten to twelve days. The real problem in containing transmission, however, is that people who never develop any symptoms whatsoever can also infect others for a roughly similar period.

Fourth, and finally, the viruses differ in the fourth dimension—time. The incubation period for influenza is generally one to three days, and most people get sick on day two; for Covid-19 the incubation period ranges from two to fourteen days and most people get sick on day five or six. Influenza symptoms come on suddenly, all at once, and people are usually sick for three or four days although recovery can sometimes drag on for several weeks. Covid-19 comes on gradually; it may take over a week after the first symptoms before serious complications such as shortness of breath develop, but then deterioration can be very rapid. Recovery also takes longer; for too many, including those who never became sick enough to require hospitalization, recovery takes long enough that “long Covid” names a syndrome for people who suffer in one way or another for months. Each generation of the disease—transmission from one person to another to another to another—also takes longer. Influenza in 1918, and seasonal influenza, passes through a given community generally in six to ten weeks. The duration of a Covid-19 outbreak, even without taking such measures to interrupt transmission as shutting down much of the economy, would stretch out for many months; those measures both save lives and lead to a faster and stronger economic recovery, but they also make the outbreak last longer than it would otherwise.

As a result, many young adults do not feel vulnerable even though they may suffer unknown long-term consequences of the disease, and Covid-19 has inflicted tremendous economic damage, far more than the steep but brief recession in 1918.

The two viruses also have one other commonality. In 1918 the United States government minimized the disease out of concern that the truth would damage the war effort. In 2020, the White House repeatedly and over a period of months minimized the threat and pushed states to reopen too soon.

These three things—that the young get less sick, that the economy has suffered, that the administration minimized the threat—combined to eviscerate the public health response. At this writing, the United States, population of 325 million, has four times the daily death toll of the European Union and the United Kingdom with their combined population of 510 million. The US economic recovery also lags far behind that of Europe.

What will happen in the future? How resilient will the US prove to be? Government at every level, federal, state, and local, has lost tax revenues and had dramatically increased costs, creating fiscal pressures not seen since World War II. What that means for tax and spending policies at every level remains to be seen. Small businesses have been decimated, and many will close permanently. Great industries such as transportation, particularly airlines, and tourism have been dealt devastating blows. Changes in work habits may reshape commercial real estate and public transit.

All that and more may come to pass—or it may not. If we develop a highly effective vaccine and distribute it rapidly, we may return to a pre-pandemic normal sooner rather than later, or we could see something in-between the old normal and a radical reshaping of society. Which future will it be? It is impossible to predict.

John M. Barry is the prize-winning author of several books, including Roger Williams and the Creation of the American Soul: Church, State, and the Birth of Liberty (2012) The Great Influenza: The Story of the Deadliest Pandemic in History (2004) Power Plays: Politics, Football, and Other Blood Sports (2001), and Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America (1997).