Nearly 15 million people were killed either by COVID-19 or by its impact on overwhelmed health systems during the first two years of the pandemic, the World Health Organisation (WHO) estimates.
The estimate is more than double the current official death toll of just over six million.
Most of the deaths occurred in Southeast Asia, Europe and the Americas, according to a WHO report issued on Thursday.
Director-General of the United Nation's health agency, Tedros Adhanom Ghebreyesus, said the newly calculated figure was "sobering" and should prompt countries to invest more in their capacities to quell future health emergencies.
WHO tasked scientists with determining the actual number of COVID-19 deaths between January 2020 and the end of last year.
They estimated between 13.3 million and 16.6 million people died either due to the coronavirus directly or because of factors linked to the pandemic's impact on health systems, such as cancer patients who were unable to seek treatment when hospitals were full of COVID-19 patients.
Indonesia has one of the highest COVID-19 death tolls in South East Asia. (Photo by Wisnu Prasetyo / SOPA Images/Sipa USA) Source: AAP / SOPA Images/Sipa USA
The estimate is based on country-reported data and statistical modelling, but only about half of the countries provided information.
WHO said it was not yet able to break down the data to distinguish between direct deaths from COVID-19 and those related to the effects of the pandemic, but the agency plans a future project examining death certificates.
Accurately counting COVID-19 deaths has been problematic throughout the pandemic, as reports of confirmed cases represent only a fraction of the devastation wrought by the virus, largely due to limited testing.
Government figures reported to WHO, and a separate tally kept by Johns Hopkins University in the United States, show more than 6.2 million reported virus deaths to date.
For a study in medical journal Lancet, scientists at the Institute of Health Metrics and Evaluation at the University of Washington calculated there were more than 18 million COVID deaths from January 2020 to December 2021.
A team led by Canadian researchers estimated there were more than three million uncounted coronavirus deaths in India alone.
A COVID-19 patient breathing with the aid of an oxygen mask in India. Source: AAP
In a statement following the release of WHO's data, India disputed the agency's methodology.
India's Health and Family Welfare Ministry called the analysis and data collection methods "questionable" and complained the new death estimates were released "without adequately addressing India's concerns."
Dr Samira Asma, a senior WHO director, acknowledged that "numbers are sometimes controversial" and noted all estimates are only an approximation of the virus's catastrophic effects.
"It has become very obvious during the entire course of the pandemic, there have been data that is missing," Dr Asma said on Thursday.
"Basically, all of us were caught unprepared."
Dr Bharat Pankhania, a public health specialist at Britain's University of Exeter, said the world may never get close to measuring the true toll of COVID-19, particularly in poor countries.
"When you have a massive outbreak where people are dying in the streets because of a lack of oxygen, bodies were abandoned or people had to be cremated quickly because of cultural beliefs, we end up never knowing just how many people died," he explained.
Dr Pankhania said while the estimated COVID-19 death toll still pales in comparison to the 1918 Spanish flu pandemic - which experts estimate caused up to 100 million deaths - the fact that so many people died despite the advances of modern medicine, was shameful.
He also warned the cost of COVID-19 could be far more damaging in the long term, given the increasing burden of caring for people with long COVID.
Staff treat patients at a COVID-19 ward at King's College Hospital in south east London. Source: AAP
"There was not an enduring immunological condition that we're seeing right now with COVID.
"We do not know the extent to which people with long COVID will have their lives cut short and if they will have repeated infections that will cause them even more problems."
