Modeling Study Finds COVID-19 Vaccines Prevented 20 Million Deaths Globally In First Year of Availability

In the first modeling study to quantify the impact of COVID-19 vaccines on a global scale, experts estimate that 19.8 million out of a potential 31.4 million deaths were prevented in the first year after vaccines were introduced.

Furthermore, the study, published in The Lancet Infectious Diseases, estimates that an additional 599,300 lives could have been saved if the World Health Organization (WHO) goal of vaccinating 40% of the population in each country with 2 or more doses by the end of 2021 had been met. The study is based on data from 195 countries and territories and is the first to assess deaths averted directly and indirectly as a result of COVID-19 vaccination, according to the authors.

“Our findings offer the most complete assessment to date of the remarkable global impact that vaccination has had on the COVID-19 pandemic,” said lead author Oliver Watson, PhD, in a press release. “Of the almost 20 million deaths estimated to have been prevented in the first year after vaccines were introduced, almost 7.5 million deaths were prevented in countries covered by the COVID-19 Vaccine Access Initiative (COVAX).”

Since the first COVID-19 vaccines were administered outside of a clinical trial setting on December 8, 2020, almost 66% of the world’s population has received at least 1 dose, according to the study. The COVAX program has facilitated access to affordable vaccines for lower income countries in an effort to reduce disparities, with an initial target of administering 2 vaccine doses to 20% of the population in countries covered by COVAX by the end of 2021. This target was later expanded by WHO, with the goal of fully vaccinating 70% of the world’s population by mid-2022.

Despite the speed of global vaccine rollout, more than 3.5 million COVID-19 deaths have been reported since the first vaccine was administered in December 2020. Several studies have tried to estimate the impact of vaccinations on the pandemic, though most have focused on specific countries, states, or cities, rather than the global impact.

“Quantifying the impact that vaccination has made globally is challenging because access to vaccines varies between countries, as does our understanding of which COVID-19 variants have been circulating, with very limited genetic sequence data available for many countries,” said co-first author Gregory Barnsley in the press release. “It is also not possible to directly measure how many deaths would have occurred without vaccinations. Mathematical modelling offers a useful tool for assessing alternative scenarios, which we can’t directly observe in real life.”

To estimate the impact of global vaccination efforts, researchers used an established model of COVID-19 transmission using country-level data for officially recorded COVID-19 deaths occurring between December 8, 2020, and December 8, 2021. Analyses were compared with an alternative hypothetical scenario in which no vaccines were delivered.

Based on officially recorded COVID-19 deaths, researchers found that an estimated 18.1 million deaths would have occurred during the study period if vaccinations had not been distributed. Of these, the model estimates that vaccination has prevented 14.4 million deaths, representing a global reduction of 79%.

Notably, these findings do not account for under-reporting of COVID-19 deaths, which is common in lower income countries. The researchers did a further analysis based on total excess deaths during the same time period to account for this. They found that COVID-19 vaccination prevented an estimated 19.8 million deaths out of a total of 31.4 million potential deaths that would have occurred without vaccination, which marks a 63% reduction, according to the study.

More than three-quarters (79%) of deaths averted were attributed to the direct protection against severe symptoms provided by vaccination, leading to lower mortality rates. The remaining 4.3 million prevented deaths were estimated to have been prevented by indirect protection from reduced transmission of the virus in the population and reduced burden on health care systems.

The researchers also found that vaccine impact changed over time and in different areas of the world as the pandemic progressed. In the first half of 2021, the greatest number of deaths averted by vaccination was seen in lower middle-income countries, as a result of the significant epidemic wave seen in India as the Delta variant emerged. This trend then shifted to the greatest impact being concentrated in higher income countries during the second half of 2021, as restrictions on travel and social gatherings were relaxed.

Overall, the number of estimated deaths prevented per person was greatest in high income countries, reflecting the earlier and wide rollout of vaccines in these areas. High and upper-middle income countries accounted for the greatest number of deaths averted, illustrating inequalities in access to vaccines around the world.

Of the 83 countries included in the analysis that are covered by COVAX, an estimated 7.4 million deaths were averted out of a potential 17.9 million (41%). However, failure to meet the goal of vaccinating 20% of the population in some countries is estimated to have resulted in an additional 156,900 deaths. These deaths were concentrated in 31 African countries, where 123,700 deaths could have been prevented if the target had been met, according to the study.

Similarly, researchers found that the failure to meet the WHO target of fully vaccinating 40% of the population of each country by the end of 2021 is estimated to have contributed to an additional 599,300 deaths worldwide that could have been prevented. Lower-middle income countries accounted for most of these deaths, according to the study.

“Our study demonstrates the enormous benefit that vaccines had in reducing deaths from COVID-19 globally,” said Azra Ghani, MBE, FMedSci, chair in infectious disease epidemiology at Imperial College London, in the press release. “Whilst the intense focus on the pandemic has now shifted, it is important that we ensure the most vulnerable people in all parts of the world are protected from ongoing circulation of COVID-19 and from the other major diseases that continue to disproportionately affect the poorest.”

REFERENCE

The Lancet Infectious Diseases: COVID-19 vaccines are estimated to have prevented 20 million deaths worldwide in the first year of the vaccine program, modelling study finds. News release. EurekAlert; June 23, 2022. Accessed June 28, 2022. https://www.eurekalert.org/news-releases/956782