The pandemic's effects on mortality have been uneven. Life expectancy dipped in most places last year, shaving 28.1 million years off the cumulative longevity in 31 countries. But residents of a handful of places that successfully kept Covid-19 at bay -- including New Zealand and Taiwan -- actually lived longer.

Life expectancy is an indication of how long on average people will live once their age is taken into account, provided that there aren't any big shifts in the number of people dying in each age bracket over time. Another measure -- excess years of life lost -- quantifies the impact when those changes do occur, and gives greater weight to deaths that occur at younger ages.

A study of 37 countries and territories in the journal BMJ found the pandemic was a killing field in most places. More than 28 million years of life were lost in 2020 across 31 of them, with Russia, Bulgaria, Lithuania, the U.S., and Poland recording the heaviest toll, the study led by Nazrul Islam, a physician-epidemiologist and medical statistician at the University of Oxford, found.

Years of life lost in 2020 were higher than expected everywhere except Taiwan, New Zealand, Norway, Iceland, Denmark, and South Korea.

The number of years of life lost due to Covid-19 was more than five times greater than those lost from influenza in 2015, during the worst seasonal flu epidemic since the turn of the century.