VSCovid-19 vaccines more than halved the potential number of deaths worldwide in the first year of their availability, according to a study published Thursday in The Lancet Infectious Diseases.
The study modeled the spread of the disease in 185 territories and countries and found that without Covid vaccines, 31.4 million people would have died from the disease between December 2020 and 2021. As the pandemic wreaked havoc in worldwide, with more than 3.5 million deaths since the first vaccine was administered in December 2020, the study estimates that vaccinations have also prevented 19.8 million deaths.
“We knew it would be a big number, but I didn’t think it would be as high as 20 million deaths in the first year alone,” said Oliver Watson, a fellow at Imperial College London and the London School of Hygiene and Tropical Medicine and co-first author of the study.
However, millions more deaths could have been prevented. The team found that one in five deaths from Covid-19 in low-income countries could have been prevented if the World Health Organization’s global vaccination targets had been met.
The team applied a Covid transmission model, incorporating what we now know about the disease and vaccines, to three situations: one in which no vaccine was available, one in which vaccines were given but failed. not reduce transmission, and third, the scenario that actually rolled out, with effective vaccines rolled out – in some parts of the world – in record time.
Then they took the number of Covid deaths estimated in the first situation – if no vaccine existed – and subtracted the number of Covid deaths observed in the third situation to determine how many deaths were averted.
It’s an approach that assumes the transmission of Covid-19 is the same from country to country, which isn’t necessarily the case, noted Émilie Koum Besson, a researcher at the London School who doesn’t was not affiliated with the study. Still, the research offers new insight into how many lives Covid-19 vaccinations could have saved.
Because many Covid deaths have gone unrecorded or unreported, particularly in low-income countries, the authors chose to examine a measure known as excess mortality, which calculates the difference between the number of deaths observed and expected in a country. For countries not included in the excess mortality database they used, the study used projections of a model developed by The Economist. The authors were unable to calculate excess mortality for some countries, including Iraq and Sudan.
“Having estimates of excess mortality for each country was critical for this study and allowed us to try to better understand the true size of the pandemic in many low-income countries,” Watson said.
They also modeled the impact of vaccinations using a Johns Hopkins Database officially declared deaths. When the model was fitted to these officially reported Covid deaths, they found that 14.4 million deaths were averted by vaccines, a more conservative estimate than that calculated using excess mortality.
The actual number of deaths averted is “probably somewhere in between, although it’s not necessarily that simple,” according to Gregory Barnsley, research assistant and co-first author of the study. Barnsley said the excess mortality could include deaths unrelated to Covid and that there are complications in determining Covid as the cause of death in people with multiple morbidities.
Additionally, the study explains that while the majority of the benefits of vaccines came from direct protection – individuals are less likely to become infected or die from the disease after vaccination – there is also some degree of indirect protection. In other words, vaccines reduce transmission in a population, relieving some pressure on hospital resources and, potentially, making it easier to care for the sickest patients.
“A vaccination is not just for people,” said Koum Besson. “It’s really for the health care system and for the environment.”
The team used national-level aggregated data on first- and second-dose vaccine uptake and quantified vaccine effectiveness based on the predominant vaccine type in each country. All of their data and code is publicly available. Their work has limitations, including a lack of genetic sequencing data to confirm the frequency of circulating variants, uncertainty about the effectiveness of vaccines, and an inability to explain how governments would likely change lockdown policies or restrictions. travel.
The researchers also assessed two additional scenarios. The first is what would have happened if all countries covered by the Advance Market Commitment of the COVID-19 Vaccine Access initiative – a scheme incentivizing manufacturers to provide donor-funded Covid vaccines to 92 low-income countries low and intermediate – had been able to vaccinate at least 20% of their population. The other estimated 40% vaccination coverage for all countries, which is the target set by the WHO.
They found that 41 countries did not meet the COVAX target and 96 countries did not meet the WHO threshold. Koum Besson said these findings underscore the need to examine who is responsible for gaps in global access to vaccines – and who has the power to change them. However, this is difficult to examine given the limited data available in some parts of the world.
“The paper talks about global estimates, but most of the background literature and information comes from Western institutions,” she said.
Watson said there are clear, albeit challenging, steps to improve the impact of Covid vaccines: scale up vaccine delivery infrastructure, increase confidence in vaccines and hold political leaders accountable for vaccine donations.