Covid has caused the loss of 28m years of life, according to the largest-ever survey to assess the scale of the impact of the pandemic.

The enormous toll was revealed in research, led by the University of Oxford, which calculated the years of life lost (YLL) in 37 countries. The study measured the number of deaths and the age at which they occurred, making it the most detailed assessment yet of the impact of Covid-19.

Alongside significant falls in life expectancy in most countries, the number of years lost from premature deaths soared. Researchers said the true toll was likely to be even higher as they did not include most countries from Asia, Africa and Latin America in the study, due to a lack of data.

Dr Nazrul Islam, of Oxford’s Nuffield Department of Population Health, who led the study, said he and his team were “shocked” by the findings, which were published in the medical journal the BMJ.

“We had to stop at one point to go over everything,” said Islam, who has himself lost relatives and colleagues to Covid. Despite having personal experience of the impact of the disease, Islam was still taken aback by the figures. “Nothing has shocked me so much in my life as the pandemic,” he said.

Researchers said understanding the full impact of Covid, the worst public health crisis in a century, required not only the counting of excess deaths, but also analysing how premature those deaths were. Using the YLL measure, an international team of researchers, led by Oxford’s Islam, estimated the changes in life expectancy and excess years of life lost from all causes in 2020.

They compared the observed life expectancy and years of life lost in 2020 with those that would be expected based on historical trends in 2005-19 in 37 upper-middle and high-income countries.

Between 2005 and 2019, life expectancy increased in men and women in all the countries studied. In 2020, there was a decline in life expectancy in men and women in every country except New Zealand, Taiwan, and Norway, where there was a gain in life expectancy, and Denmark, Iceland and South Korea, where no evidence of a change in life expectancy was found.

The highest decline in life expectancy in years was in Russia (-2.33 in men and -2.14 in women), the US (-2.27 in men and -1.61 in women) and Bulgaria (-1.96 in men and -1.37 in women).

The decline in life expectancy in years in England and Wales was -1.2 in men and -0.8 in women. In Scotland, it was -1.24 in men and -0.54 in women.

In 2020, years of life lost were higher than expected in all countries except Taiwan and New Zealand, where there was a reduction in years of life lost, and Iceland, South Korea, Denmark, and Norway, where there was no evidence of a change in years of life lost.

In the remaining 31 countries, more than 222m years of life were lost in 2020, which is 28.1m more than expected (17.3m in men and 10.8m in women).

The highest excess years of life lost per 100,000 people were in Russia (7,020 in men and 4,760 in women), Bulgaria (7,260 in men and 3,730 in women) and Lithuania (5,430 in men and 2,640 in women). In England and Wales it was 2,140 in men and 1,210 in women, while in Scotland it was 2,540 in men and 925 in women.