The World Health Organization is estimating that nearly 15 million people were killed either by the coronavirus or by its impact on overwhelmed health systems in the past two years, more than double its official death toll.

Most of the fatalities were in Southeast Asia, Europe and the Americas.

In a report released on Thursday, the U.N. agency’s chief Tedros Adhanom Ghebreyesus described the figure as “sobering." Accurate numbers on COVID-19 deaths have been problematic throughout the pandemic, as the figures are only a fraction of the devastation wrought by the virus, largely because of limited testing and differences in how countries count COVID-19 deaths.

“These sobering data not only point to the impact of the pandemic but also to the need for all countries to invest in more resilient health systems that can sustain essential health services during crises, including stronger health information systems,” said Ghebreyesus. “WHO is committed to working with all countries to strengthen their health information systems to generate better data for better decisions and better outcomes.”

The WHO said it used excess deaths as part of its calculation. Excess mortality is calculated as the difference between the number of deaths that have occurred and the number that would be expected in the absence of the pandemic based on data from earlier years, the WHO said.

As of Wednesday, nearly 1 million Americans have died as a direct result of COVID-19, Johns Hopkins University said.