The coronavirus pandemic led to one million extra deaths in 29 high-income countries in 2020, a study published on Wednesday by The BMJ said.
With the exception of Norway, Denmark and New Zealand, all other countries had more deaths than expected in 2020, particularly among men.
The five countries with the highest number of excess deaths were the US, UK, Italy, Spain and Poland.
Excess deaths have been used to mark the effects of the pandemic's since it began, but this University of Oxford study is the first to take into account temporal and seasonal trends, as well as differences in age and sex across countries.
Researchers from the university's Nuffield Department of Population Health used a mathematical model that tabulated the last five years' mortality trends in the 29 high-income countries studied.
An estimated 979,000 excess deaths occurred in these countries with America's 458,000 the most, a reflection of its sizeable population and pandemic management.
New Zealand was calculated as having 2,500 fewer deaths than in a normal year, a reflection of its success in dealing with the coronavirus.
The total number of excess deaths was largely concentrated among people aged 75 or older, followed by people aged 65-74. Deaths in children under 15 were similar to expected levels in most countries and lower than expected in others.
In most countries, the estimated number of excess deaths exceeded the number of reported deaths from Covid-19. For example, in both the US and the UK, estimated excess deaths were more than 30 per cent higher than the number of reported Covid deaths.
Contrastingly, Israel and France had a higher number of reported Covid deaths than estimated excess deaths, which the researchers tentatively ascribed to reporting differences.
Excess death rates higher in men than women
In most countries, age-specific excess death rates were higher in men than in women, and the absolute difference in rates between the sexes tended to increase with age.
The US was an outlier on this metric, however, as its excess death rate was higher among women than men in those aged 85 or older.
Researchers said the study did have some limitations, and cited a lack of data from lower and middle-income countries.
They warned that Covid's full impact may not be apparent for many years, particularly in lower-income countries where factors such as poverty, lack of vaccines, weak health systems and high population density place people at increased risk.
"There is an urgent need to measure this excess morbidity, support those with long-term complications of Covid-19 and fund health systems globally to address the backlog of work resulting from the pandemic," they said.
More work is required from the researchers, too, if they are to understand the impact of national vaccination programmes on mortality in 2021.
