India's excess Covid-19 deaths could be 10 times the official count, according to the most comprehensive research conducted on the effect of the virus in the country.

The new report analyzed data from three different sources to draw the most extensive picture to date, of how the pandemic has affected India

"India's official death count as of end-June 2021 is 400,000," the report said. "The reality is, of course, catastrophically worse."

"What is tragically clear is that too many people, in the millions rather than hundreds of thousands, may have died."

Excess deaths are calculated by determining how many more people died than usual over a specific time period. While the virus is unlikely to account for all of the excess deaths that occurred during the pandemic, it is likely that it contributed to a considerable number of them.

The paper concedes that determining an exact death toll may "prove elusive," but that one "is likely to be an order of magnitude greater than the official count."

Arvind Subramanian, the former chief economic adviser to the India government, and two other experts from the Center for Global Development and Harvard University published the report.

He said that the figure could have overlooked deaths that happened in overcrowded hospitals or when health care was disrupted, particularly during the devastating virus surge earlier this year.

State governments and local governments across India have been accused of purposely undercounting Covid-19 deaths, and because the virus's stigma stopped many people from getting tested, many deaths went unrecorded as virus fatalities.

Following public criticism and accountability requests, some India states have revised their mortality figures, resulting in a significant increase in the official death toll.

"How can we have a basic understanding of the effect of the virus without knowing how many people died and where they died?" Subramanian said. "Accurate data is the only way we can prepare a fully-fledged response to the pandemic in the future."