David Adam in Nature:
Last year’s Day of the Dead marked a grim milestone. On 1 November, the global death toll from the COVID-19 pandemic passed 5 million, official data suggested. It has now reached 5.5 million. But that figure is a significant underestimate. Records of excess mortality — a metric that involves comparing all deaths recorded with those expected to occur — show many more people than this have died in the pandemic.
Working out how many more is a complex research challenge. It is not as simple as just counting up each country’s excess mortality figures. Some official data in this regard are flawed, scientists have found. And more than 100 countries do not collect reliable statistics on expected or actual deaths at all, or do not release them in a timely manner.
Demographers, data scientists and public-health experts are striving to narrow the uncertainties for a global estimate of pandemic deaths.