June 24, 2022 -- Vaccinations prevented nearly 20 million deaths from COVID-19 in 185 countries and territories in the first 12 months the shots were available, a mathematical modeling study calculates.

The study, co-led by Oliver J. Watson, PhD, and Gregory Barnsley, MSc, with the MRC Centre for Global Infectious Disease Analysis, Imperial College London in London, England, was published online Thursday in The Lancet Infectious Diseases.

Researchers estimated that vaccines prevented 14.4 million deaths from COVID in the countries and territories between December 8, 2020, and December 8, 2021.

But the estimate rose to 19.8 million deaths from COVID averted when excess deaths were added to the equation.

"[W]e used excess deaths as an estimate of the true extent of the pandemic, representing a global reduction of 63% in total deaths (19.8 million of 31.4 million) during the first year of COVID-19 vaccination," the authorswrote. .

In 1 Year, Nearly Half the World Had Two Doses

The first dose of a COVID vaccine outside of a clinic was given December 8, 2020, and 1 year later, the researchers estimated, 55.9% of the global population had received at least one dose, 45.5% had two, and 4.3% had a booster. But coverage has vastly varied in different parts of the world.

For the 83 countries in the study covered by the COVAX commitment to affordable vaccines, an estimated 7.4 million deaths were averted out of a potential 17.9 million (41%).

But in countries that failed to meet the COVAX target of fully vaccinating 20% of the population, researchers estimated an additional 156,900 died from COVID.

Though a small part of the global deaths, these preventable deaths were clustered in 31 African nations, where 132,700 deaths could have been averted if those targets had been met, the researchers report.

The authors calculate that a further 599,300 lives could have been saved if the World Health Organization's target of vaccinating 40% in each country with two or more doses by the end of 2021 had been met.

In an accompanying editorial, Chad R. Wells, PhD, and Alison P. Galvani, PhD, both with the Yale Center for Infectious Disease Modeling and Analysis in New Haven, CT, wrote, "Meeting these targets, particularly in low-income countries, is challenged by myriad obstacles that require international support to overcome."

Among them are that several high-income countries got advanced purchasing agreements for the vaccines, while low-income countries couldn't afford those prices, they noted. In the United States, the number of doses purchased before production "was enough to fully vaccinate its entire population three times over," they said.

Meanwhile, in Burundi, rollout started 10 months after the U.S., wrote Wells and Galvani, who were not part of the study.

First to Calculate Deaths Averted Globally

Previous studies have looked at deaths averted by countries or other geographic areas. This is the first to calculate lives saved directly or indirectly on a global scale.

There are several limitations with the study, the authors acknowledged. The calculations rely on assumptions including proportions of which vaccine types were delivered in each country, how they were delivered, and the precise timing of when new virus variants arrived.

Researchers also assumed that the relationship between age and the proportion of COVID-19 deaths occurring among infected people is the same for each country. Additionally, countries differ in the ways they report deaths from COVID-19.

"Our findings offer the most complete assessment to date of the remarkable global impact that vaccination has had on the COVID-19 pandemic.... However, more could have been done. If the targets set out by the WHO had been achieved, we estimate that roughly 1 in 5 of the estimated lives lost due to COVID-19 in low-income countries could have been prevented," said Watson, in a press release.