A new report by the World Health Organization estimates that the COVID-19 pandemic had killed nearly 15 million people globally by the end of last year, more than double the previous tally of more than 6 million.

The United States likely already has passed the grim milestone of 1 million deaths, according to the tally that included both people who died from COVID infections and as a result of its impact on health-care systems.

Obtaining a perfectly accurate count of the number of lives lost as a result of the pandemic is virtually impossible, health experts said. The availability of testing, difficulty diagnosing COVID early in its spread, and even how doctors fill out death certificates all play roles in obfuscating a precise death count.

For example, the latest official count from the Centers for Disease Control and Prevention stands at 993,341 deaths.

The WHO report included an additional 107,407 estimated U.S. deaths as of December 2021, or 13% more deaths than the CDC was reporting.

“It helps you understand what the total magnitude was of this pandemic,” said Amesh A. Adalja, a doctor and senior scholar for the Johns Hopkins Center for Health Security. “When you think about preparing for the next pandemic, these numbers are really useful to have.”

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The WHO used statistical modeling to calculate excess deaths from January 2020 to December 2021 by comparing deaths during the pandemic with the years prior.

The WHO’s count, Adalja said, captures the full consequence of the pandemic. It caused people to put off cancer treatments, mammograms, or child vaccinations, or allowed malaria controls to lapse.

“It shows just how the pandemic impacted human civilization,” he said. “In the midst of a pandemic, it’s very difficult to get highly accurate numbers, especially when you’re talking about the world or places with very poor public health infrastructure.”

In some parts of the world, particularly in poor countries, people died in the streets or bodies were abandoned or cremated quickly before a COVID infection could be confirmed, said Dr. Bharat Pankhania, a public health specialist at Britain’s University of Exeter.

“We end up never knowing just how many people died,” he explained.

Scientists estimated from 13.3 million to 16.6 million people died either due to the coronavirus directly or because of factors somehow attributed to the pandemic’s impact on health systems, such as cancer patients who were unable to seek treatment when hospitals were full of COVID patients.

Based on that range, the scientists came up with an approximated total of 14.9 million. That number includes deaths that resulted from overwhelmed health-care systems, or people’s reluctance to seek treatment due to fear of COVID — but the WHO was working on further analysis to distinguish those from deaths directly attributable to the virus.

Most of the deaths occurred in Southeast Asia, Europe, and the Americas, according to the WHO report.

The U.N. health agency’s director-general, Tedros Adhanom Ghebreyesus, described the newly calculated figure as “sobering,” saying it should prompt countries to invest more in their capacities to quell future health emergencies.

Unavoidable imprecision in counts

Calculating COVID’s true toll has been a challenge since the beginning of the pandemic. In July 2020, a Yale University study estimated that the U.S. undercounted its COVID deaths by 28% due to poor availability of testing and imprecise records of people’s causes of death.

Experts say imprecision is unavoidable when dealing with large-scale disasters like pandemics. The Spanish flu’s estimated 100 million deaths in 1918 is likely a significant undercount, according to Hopkins’ Adalja. Many doctors at the time didn’t realize the illness was the result of a virus. The U.S. death count has gotten more accurate since the start of the COVID-19 pandemic, he said.

Even now, inaccurate death certificates likely continue to undercount the number of COVID deaths, said Gregory McDonald, chair of the forensic medicine and pathology department at the Philadelphia College of Osteopathic Medicine.

“You have such an inconsistency of reporting, an inconsistency of documentation, an inconsistency in filling out death certificates — not only in a single state, but you’re talking all over the world,” McDonald said.

There are two ways COVID could be recorded in a death certificate, McDonald said, either as the primary cause of death, such as a person who was healthy until contracting COVID, or as a contributing cause. For patients who suffer from other ailments, such as cancer or heart conditions, doctors may leave out COVID as a contributing cause. In some cases, people with terminal illnesses may be near death but would have lived a little longer if they hadn’t contracted the virus.

“I’ve been having some cases I’ve reviewed where I would have put COVID in that contributing factor,” McDonald said. “There are a ton of cases out there that will never be analyzed or evaluated.”

Pandemic at transition point

Even as the WHO released its recent calculations, health experts noted the number will need to be revised.

“We’re sort of in general at a transition point in the United States and in some of the industrial countries,” Adalja said, “but there will still be more deaths from the pandemic.”

In Pennsylvania and New Jersey, hospital admissions of people with COVID have increased over the last two weeks. Pennsylvania appeared likely to hit 1,000 people hospitalized with the virus in the coming days. New Jersey reported close to 600 people hospitalized with the virus, according to data from the New York Times. Pennsylvania was averaging 15 deaths per day and New Jersey was averaging seven as of Wednesday. The states have reported a combined death toll of 78,200 people.

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So many lives have been lost, Adalja said, in part because public health agencies looked at the H1N1 pandemic in 2009 as the worst a worldwide viral outbreak could be in modern times. That virus killed between 8,868 to 18,306 Americans and up to an estimated 575,000 worldwide, according to the CDC.

“There was a lot of complacency after the 2009 pandemic,” he said.

The WHO’s most recent count, described by a senior director there as an approximation, is also likely to be one of several estimates that will emerge as the world takes stock of COVID’s impact.

The Institute of Health Metrics and Evaluation at the University of Washington estimated 18 million COVID deaths from January 2020 to December 2021. Another team led by Canadian researchers estimated there were more than 3 million uncounted coronavirus deaths in India alone. The WHO’s analysis estimated between 3.3 million to 6.5 million. Health experts will continue to fine-tune the count to reach a more accurate measure of COVID-19′s lethality.

“I think it’ll be more precise than 1918, but there probably will be adjustments and debates over what the actual scope was,” Adalja said. “I think people will come to a consensus range for where it actually stands.”

Staff writer Justine McDaniel and the Associated Press contributed to this article.