In the first year of the vaccination programme, 19.8 million out of a potential 31.4 million Covid-19 deaths were prevented worldwide, according to estimates based on excess deaths from 185 countries and territories, the researchers said.
A study published in the Lancet Infectious Diseases Journal found that the Covid-19 vaccines reduced the potential death toll during the pandemic by nearly 20 million (1 million = 10 lakhs) or more than half in the year following their implementation while in India, Covid-19 vaccines prevented over 42 lakh potential deaths in 2021.
The study was based on a mathematical modelling which focused on estimates of "excess" mortalities in the country during the pandemic.
In the first year of the vaccination programme, 19.8 million out of a potential 31.4 million Covid-19 deaths were prevented worldwide, according to estimates based on excess deaths from 185 countries and territories, the researchers said.
The study estimates a further 5,99,300 lives could have been saved if the World Health Organisation's target of vaccinating 40 per cent of the population in each country with two or more doses by the end of 2021 had been met.
The study estimated the number of deaths that were prevented between December 8, 2020 and December 8, 2021, which reflects the first year in which the vaccines were distributed.
"For India, we estimate that 42,10,000 deaths were prevented by vaccination in this period. This is our central estimate, with the uncertainty in this estimate ranging between 36,65,000-43,70,000," lead author of the study, Oliver Watson from the Imperial College London, the UK, told reporters
"What this modelling study shows is that the vaccination campaign in India has likely saved millions of lives. This shows the remarkable impact that the vaccination has had, especially in India, which was the first country to experience the impact of the Delta variant," Watson said in an email.
The India numbers are based on the estimates that 51,60,000 (48,24,000-56,29,000) deaths may have occurred in the country during the pandemic, a number which is 10 times the official figure of 5,24,941 deaths reported so far, he said.
"These estimates are based on the estimates of excess mortality in India during the Covid-19 pandemic, which we have sourced from The Economist and are similar to the estimates that the WHO have reported. Independently, our group has also investigated the COVID-19 death toll based on reports of excess mortality and seroprevalence surveys and arrived at similar estimates of almost 10 times the official count," Watson said.
The WHO had last month estimated that there were 4.7 million Covid-linked deaths in India, a figure that was refuted by the government.
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), the researchers said.
COVAX was set up because it was clear early on that global vaccine equity would be the only way out of the pandemic, they said.
The initiative has facilitated access to affordable vaccines for lower income countries to try to reduce inequalities, with an initial target of giving both vaccine doses to 20 per cent of the population in countries covered by the commitment by the end of 2021, the researchers said.Since the first COVID-19 vaccine was administered outside of a clinical trial setting on December 8, 2020, almost two-thirds of the world's population has received at least one dose of a COVID-19 vaccine (66 per cent), they noted.
Despite the incredible speed of the vaccine roll-out worldwide, more than 3.5 million Covid-19 deaths have been reported since the first vaccine was administered in December 2020, they said.
To estimate the impact of the global vaccination programmes, the 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.
To account for under-reporting of deaths in countries with weaker surveillance systems, they carried out a separate analysis based on the number of excess deaths recorded above those that would have been expected during the same time period.
China was not included in the analysis owing to its large population and very strict lockdown measures which would have skewed the findings, the researchers said.
The team found that based on officially recorded Covid-19 deaths, an estimated 18.1 million deaths would have occurred during the study period if vaccinations had not been implemented.
Of these, the model estimates that vaccination has prevented 14.4 million deaths, representing a global reduction of 79 per cent.
These findings do not account for under-reporting of Covid-19 deaths, which is common in lower income countries.
The team 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, a reduction of 63 per cent.
More than three quarters (79 per cent) of deaths averted were due to the direct protection against severe symptoms provided by the vaccination, leading to lower mortality rates, the researchers said.
The remaining 4.3 million averted deaths were estimated to have been prevented by indirect protection from reduced transmission of the virus in the population and reduced burden on healthcare systems, thereby improving access to medical care for those most in need, they said.
The study found that the 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, resulting from the significant epidemic wave in India as the Delta variant emerged.
This subsequently shifted to the greatest impact being concentrated in higher income countries in the second half of 2021, as restrictions on travel and social mixing were eased in some areas leading to greater virus transmission.
The shortfall in the WHO target of fully vaccinating 40 per cent of the population of each country by the end of 2021 is estimated to have contributed to an additional 5,99,300 deaths worldwide that could have been prevented.
Lower-middle income countries accounted for the majority of these deaths.
"Our study demonstrates the enormous benefit that vaccines had in reducing deaths from Covid-19 globally," said Professor Azra Ghani, Chair in Infectious Disease Epidemiology at Imperial College London.
"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," Ghani said.
The authors note several limitations to their findings. Notably, their model is based on a number of necessary assumptions, including the precise proportions of which vaccine types have been delivered, how they were delivered and the precise timing of when new virus variants arrived in each country.
They also assumed that the relationship between age and the proportion of Covid-19 deaths occurring among infected individuals is the same for each country.