betty June 24, 2022

SINGAPORE – Vaccinations more than halved the potential global death toll due to Covid-19, as an estimated 19.8 million deaths were averted in the first year after vaccines were introduced, according to a mathematical modelling study just published in The Lancet Infectious Diseases.

These reductions were concentrated in high income countries that relied on their vaccination programmes to relax interventions and allow SARSCoV-2 transmission to increase as they moved into a new stage of the pandemic, the authors said.

The researchers from Imperial College in London estimated that 31.4 million people would have died, if no one had been vaccinated in the first year of vaccination, beginning Dec 8, 2020.

“However, because of vaccination, we estimate that 19.8 million of these lives were saved,” said the study’s lead author, Dr Oliver Watson.

The estimates were based on excess deaths from 185 countries and territories. China was not included in the analysis owing to its large population and very strict lockdown measures, which would have skewed the findings.

The excess deaths, which are deaths that occur over and beyond what they typically are in a year without a pandemic, could have been caused directly or indirectly by the coronavirus.

Many lower-middle income countries were not able to meet vaccine targets in the first year after they were introduced, and as a result, lost hundreds of thousands of lives.

The study estimated that 156,900 additional deaths would have been averted if the vaccination target of 20 per cent set by global vaccine-sharing initiative Covax had been reached in that time frame, and a further 599,300 deaths would have been averted if the World Health Organisation’s (WHO) 2021 Covid-19 vaccination target of 40 per cent of each country’s population had been reached.

Dr Watson said in a release that, “If the targets set out by the WHO had been achieved, we estimate that roughly one in 5 of the estimated lives lost due to Covid-19 in low-income countries could have been prevented.”

More than three quarters of the 19.8 million deaths averted were due to the protection directly provided by vaccination against severe symptoms.

The remaining 4.3 million averted deaths were estimated to have had indirect protection because the use of vaccines led to reduced transmission of the virus in the population and the burden on healthcare systems, thereby improving access to medical care for those most in need.

The indirect protection extended to both vaccinated and unvaccinated individuals, said Dr Watson. First, populations with high vaccination coverage will have fewer transmission events, which reduces the likelihood of an individual encountering someone with an infection, he said.

Second, individuals who are vaccinated but still become infected are likely to be less infectious than if they did not have a vaccine. This reduces how likely they are to lead to onward infections, he added.

The latest study is the first to estimate the impact of Covid-19 vaccinations on a global scale and the first to assess the number of deaths averted both directly and indirectly.

“Such studies are absolutely necessary in health policy to determine the extent of preventable morbidity and mortality,” said Professor Teo Yik Ying, dean of the Saw Swee Hock School of Public Health at the National University of Singapore.