The official pandemic toll is 4,140,700 deaths, but the dreadful cost is most certainly higher — perhaps twice the official estimates or more.

Does it matter whether 8 or 10 million have died instead of 4 million? It does. To cope with a disaster requires knowing the true size and scope. This is essential to an effective public health system. The big lesson of the pandemic is that these systems were unready when catastrophe struck. Even wealthy nations such as the United States were caught unprepared. In the future, collecting data accurately must be a priority, along with such things as real-time disease surveillance, rapid countermeasures and strong supply chains.

A key measure, excess mortality, is the difference between the observed numbers of deaths from all causes and what would normally be expected over the same time period, absent the pandemic. This helps illuminate the true scope of the losses, and results can be startling. For example, India’s reported toll is about 419,470. But when Abhishek Anand and colleagues at the Center for Global Development looked at three different data sources, they estimated that excess mortality in India during the pandemic was “an order of magnitude” greater than the official figure, or about 3.4 million to 4.9 million deaths. Although the study cautioned that data gaps remain, they concluded that India may have misjudged the size of the first wave, when up to 2 million may have died. They conclude that “not grasping the scale of the tragedy in real time in the first wave may have bred the collective complacency that led to the horrors of the second wave.” In the United States, the covid-19 death toll is 610,387, but one recent study, by A. Danielle Iuliano and colleagues, covering Mar. 8, 2020 to May 29, 2021, found 766,611 deaths attributable to the coronavirus, of which 24 percent were not documented on death certificates, mostly among the elderly.

How can it be that so many deaths are missed? According to the World Health Organization, nearly 4 in 10 of the world’s deaths are unregistered. In Africa, only 10 percent of deaths are registered, compared to 98 percent in Europe and 91 percent in the Americas. Many people have died of the virus without having had a coronavirus test, and thus may be excluded from the official count; or they may have died at home, or from a condition indirectly linked to the pandemic, such as those who could not get medical care because hospitals were overflowing. Many lower-income countries do not have adequate data systems. China, which attempted to cover up the transmissibility of the virus in the early weeks before a draconian lockdown in Wuhan, has a reported death toll of 4,848, but that is almost certainly just a small fraction of those who died. Infections in Wuhan were estimated by one study as half a million, or 10 times the official count.

Measuring the pandemic’s toll is a tool for fighting this one and preparing for the next. All countries must do better at it.