The COVID-19 vaccines saved 20 million lives globally the first year they were available — and could have saved more if the international targets had been reached, according to a new study by researchers at the Imperial College of London.

The study, which was published Thursday in the journal Lancet Infectious Diseases, said an additional 600,000 deaths would have been prevented had the World Health Organization target of a 40% vaccination rate been reached by the end of 2021.

The first vaccine was administered on Dec. 8, 2020. But the researchers said the targets were not achieved due to vaccine shortfalls.

“Catastrophic would be the first word that comes to mind,” is how lead study author Oliver Watson described to The Associated Press what could have happened without vaccines. He said the findings “quantify just how much worse the pandemic could have been if we did not have these vaccines.”

The study found the estimated number of deaths averted was “notably higher” in high-income and upper-middle-income countries than in low-income countries, partly because they had better access to the mRNA vaccines, which proved to be very effective.

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The study’s estimates are based on data from 185 countries that showed deaths between Dec. 8, 2020, and Dec. 8, 2021. The researchers estimated that 4.2 million deaths from COVID-19 were prevented in India, 1.9 million in the United States, 1 million in Brazil, 631,000 in France and 507,000 in the United Kingdom. Researchers said they left China out of the study because of uncertainty about the country’s numbers.

The researchers used two methods to estimate deaths. In the first, which said vaccines prevented 19.8 million COVID-19 deaths, they looked at how many more deaths than usual occurred during the time period. In the second method, which said the number saved was 14.4 million, they used only reported COVID-19 deaths in the same model.

“COVID-19 vaccination has substantially altered the course of the pandemic, saving tens of millions of lives globally,” the journal article said. “However, inadequate access to vaccines in low-income countries has limited the impact in these settings, reinforcing the need for global vaccine equity and coverage.”

The Associated Press’ coverage of the study noted some limitations. “The researchers did not include how the virus might have mutated differently in the absence of vaccines. And they did not factor in how lockdowns or mask wearing might have changed if vaccines weren’t available.”

In May, the National Bureau of Economic Research published a United States-centric study of vaccine impact on COVID-19 deaths. It said state uptake of vaccines varied greatly during different time periods — for instance, from 48% in Alabama to 77% in Vermont between November 2021 and February 2022. That study said that in late 2021, “on average, one COVID death was avoided for every 124 full vaccination courses that were delivered.”

In another study of U.S. COVID-19 deaths that might have been averted, researchers at Brown University and Microsoft AI Health shared data with NPR that showed “many of the nearly 1 million COVID deaths took place in 2020 before the vaccines were available. But of the more than 641,000 people who died after vaccines were available, half of those deaths could have been averted — 318,981 — had every eligible adult gotten vaccinated.”

In some states, it said, more than half of the deaths could have been avoided. The study estimated, for instance, that 11,047 deaths in Tennessee were vaccine-preventable, as were 1,484 in Montana, 3,350 in Wyoming, 7,154 in Kentucky and 4,223 in Nevada. In other states, a lower share of deaths were preventable, such as in Utah, where 1,815 deaths might have been prevented, or 734 in Hawaii, 11,195 in New York and 21,730 in California.

The international study was funded by the World Health Organization, the UK Medical Research Council, Gavi, the Vaccine Alliance; and the Bill and Melinda Gates Foundation, National Institute for Health Research and Community Jameel.