Despite a century of medical advances, more Americans have now died from Covid-19 than the number who succumbed to the 1918 flu pandemic, according to new data.

The latest grim milestone comes as the country is experiencing a fourth-wave driven by the highly contagious Delta variant, with low vaccination uptake in many regions the main cause of death.

Johns Hopkins University tracker showed 675,722 US coronavirus deaths as of Friday, which surpasses the 675,000 US deaths during the influenza outbreak that began in the last year of World War I.

All told, some 50 million died worldwide in the flu pandemic -- sometimes inaccurately referred to as the "Spanish flu" -- making it the deadliest event in human history, according to epidemiologists.

That far exceeds global Covid deaths so far -- around 4.7 million.

But the United States has borne a disproportionate 14 percent of those fatalities, despite making up only five percent of the world's population.

The American population in 1918 was less than a third of what it is now, meaning the flu deaths would be equivalent to some 2.2 million in today's terms.

Unlike today's influenzas, which impact children and the elderly the most, the 1918 flu caused unusually high mortality among young adults.

According to the Centers for Disease Control and Prevention, with no vaccines and no antibiotics for secondary bacterial complications, control efforts were limited in the 1918-19 to non-pharmaceutical measures.