Why did a pandemic that killed upward of 50 million people, many of them otherwise healthy young adults, leave such a limited imprint on humanity’s cultural memory — especially in contrast to World War I, which killed less than half as many people.

Countless novels and films and monuments investigate or commemorate the trauma that the Great War inflicted on modern consciousness, but the Great Influenza, having torn a deadly path around the world for two years, seemed to be forgotten nearly overnight.

The global population that encountered the SARS-CoV-2 virus had grown accustomed to a world where the burden of infectious disease has been greatly reduced.

Before Covid, the most terrifying and deadly new virus to attack the United States was H.I.V., which managed to kill 100,000 Americans in its first eight years of spread here.

You could make the case that Covid will prove to be the true “great war” of the early 21st century — the source of so many genuinely new and terrifying experiences, seared into our collective memory: the hauntingly empty streets of Manhattan and Madrid, the corpses stacked in temporary freezers.

Even without public-health mandates, a significant part of the world’s population, particularly in cosmopolitan cities that were hit hard in the early days of Covid, would instantly mask up; where possible, workers would switch back to Zoom; unnecessary travel would cease.

After the Great Influenza, it took 13 years — thanks to a young virologist named Richard Edwin Shope, who noticed veterinary reports about an unusual outbreak of swine flu among pigs in fall 1918 — to prove that the pandemic had been caused by a virus at all.

The contrast with Covid could not be more extreme: We isolated the SARS-CoV-2 virus about 20 days after the outbreak was first reported.

It’s important to remember that mRNA vaccines were a promising, if unproven, line of inquiry for years before the pandemic hit; no one could say for sure that they even worked.

And just as the Great Influenza slowly nudged scientists toward the development of flu shots, which finally became commonplace in the 1940s, the Covid crisis will redirect vast sums of research dollars toward the development of universal vaccines to protect against all variants of both influenza and coronavirus?

How will it change the way we perceive the world — and its risks — when the pandemic finally subsides.