At vaccines against covid-19 reduced the potential number of global deaths during the pandemic by more than half in the year following the implementation of immunization campaigns. Estimates are from a new study of mathematical modeling published this Thursday (23) by the journal Lancet Infectious Diseases.
In the first year of the vaccination programs, averted around 19.8 million deaths worldwide out of a potential of 31.4 million deaths as a result of the disease.
Estimates were based on excess mortality from 185 countries and territories. Excess deaths is defined as the difference between the observed numbers of deaths in specific periods and the expected numbers of loss of life in the same periods.
The study estimates that an additional 599,300 lives could have been saved if the World Health Organization (WHO) target of vaccinating 40% of the population in each country, with two or more doses, by the end of 2021 had been reached.
“Our findings offer the most complete assessment to date of the remarkable global impact vaccination has had on the Covid-19 pandemic. Of the nearly 20 million deaths estimated to have been averted in the first year after vaccines were introduced, nearly 7.5 million were averted in countries covered by the Covax Vaccine Access Initiative.” Imperial College, London, in a statement.
Since the beginning of vaccination campaigns against Covid-19, the WHO has defended equity in the distribution of immunizations as a fundamental condition for facing the pandemic at a global level.
The Covax consortium, which enabled the distribution of doses against Covid-19 to low- and middle-income countries, is an initiative co-led by the Coalition for Epidemic Preparedness Innovations (CEPI), the Gavi vaccine alliance. , the WHO and the United Nations Children’s Fund (Unicef).
“Our findings show that millions of lives have likely been saved by making vaccines available to people everywhere, regardless of their wealth. Nonetheless, more could have been done . If the targets set by the WHO had been achieved, we estimate that about 1 in 5 of the lives lost due to Covid-19 in low-income countries could have been avoided,” Watson said.
Vaccination coverage
Since the first Covid-19 vaccine was administered outside a clinical trial setting on December 8, 2020, nearly two-thirds of the world’s population has received at least one dose against the disease, according to the report. lifting of the Our World in Data platform.
The Covax initiative has facilitated access to vaccines for low-income countries to try to reduce inequalities, with an initial target of providing two doses of vaccine to 20% of the population in countries covered by the commitment by the end of 2021.
The WHO has extended this target by establishing a global strategy to vaccinate 70% of the world’s population with two doses by mid-2022, with an interim target of immunizing 40% of the population in all countries by the end of 2021.
The study highlights that despite the high speed in the launch of vaccines against the disease worldwide, more than 3.5 million deaths from Covid-19 have been reported since the first immunization was administered in December 2020.
Use of mathematical modeling
Analyzes have sought to estimate the impact of vaccination on the course of the pandemic, focusing on specific regions, such as countries, states or cities. The new study published in the Lancet breaks new ground by estimating the impact of vaccination on a global scale and by assessing the number of deaths avoided directly and indirectly.
“Quantifying the impact that vaccination has had globally is challenging because access to vaccines varies between countries, as does our understanding of which coronavirus variants have been circulating, with very limited genetic sequence data available for various countries. It is also not possible to directly measure how many deaths would have occurred without vaccination.
According to the expert, mathematical modeling allows the evaluation of alternative scenarios, which cannot be observed directly in real life. To estimate the impact of global vaccination programs, the researchers used an established model of Covid-19 transmission using country-level data for officially recorded deaths from the disease between December 8, 2020 and December 8, 2021.
To account for the underreporting of deaths in countries with less robust surveillance systems, they performed a separate analysis based on the number of excess deaths recorded above those that would be expected during the same period.
Where official data were not available, the team used estimates of excessive all-cause mortality. These analyzes were then compared to an alternative hypothetical scenario where no vaccine was available.
The model took into account the variation in vaccination rates between countries, as well as differences in vaccine effectiveness within each country based on vaccine types known to have been predominantly used in those areas.
The researchers point out that China was not included in the analysis due to its large population and very strict lockdown measures, which could have skewed the findings.
What the analyzes revealed
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 vaccines had not been implemented.
Of these, the model estimates that vaccination has prevented 14.4 million deaths, representing an overall reduction of 79%. According to the study, the rates do not take into account the underreporting of deaths from the disease, which is common in low-income countries.
The team did an additional analysis based on total excess deaths during the same period. They verified that the vaccination prevented about 19.8 million deaths out of a total of 31.4 million potential deaths that would have occurred without vaccination. a reduction of 63%.
The study indicates that more than three quarters (79%, 15.5 million/19.8 million) of avoided deaths are due to the direct protection against severe symptoms provided by vaccination, leading to lower mortality rates.
It is estimated that the remaining 4.3 million deaths averted were prevented by indirect protection from reduced transmission of the virus in the population and reduction of burden on health systems , thereby improving access to medical care for those most in need.
Vaccine impacts
The vaccine’s impact changed over time and in different areas of the world as the pandemic progressed, according to the study.
In the first half of 2021, the highest number of vaccine-prevented deaths occurred in lower-middle-income countries, a result of the significant epidemic wave in India as the Delta variant emerged.
This later shifted to the greater impact concentrated in higher-income countries in the second half of 2021, as restrictions on travel and social gatherings were eased in some areas, leading to greater transmission of the virus.
Overall, the estimated number of preventable deaths per person was higher in high income countries reflecting the earlier and broader implementation of vaccination campaigns in these locations (66 deaths averted per 10,000 people in high-income countries versus 2,711 deaths averted per 10,000 people in low-income countries).
High- and upper-middle-income countries accounted for the highest number of deaths averted (12.2 million/19.8 million), highlighting the inequalities in access to vaccines all around the world.
For the 83 countries included in the analysis that are covered by the Covax consortium with affordable vaccines, an estimated 7.4 million deaths were averted out of a potential 17.9 million (41%). However, failure to meet the initiative’s target of fully vaccinating 20% of the population in some countries is estimated to have resulted in an additional 156,900 deaths.
While this number represents a small proportion of total global deaths, these preventable deaths were concentrated in 31 African nations where 132,700 deaths could have been avoided if the target had been met.
Likewise, it is estimated that the shortfall in the WHO target of fully vaccinating 40% of the population of each country by the end of 2021 has contributed to 599,300 additional deaths around the world that could have been avoided.
Lower-middle-income countries were responsible for the majority of these deaths. Regionally, most of these deaths were concentrated in the African and Eastern Mediterranean regions. If the 40% target had been met in all low-income countries, the number of vaccine-prevented deaths in these areas would have more than doubled.
“Our study demonstrates the enormous benefit that vaccines have had in reducing global deaths from Covid-19. While the intense focus on the pandemic has shifted, it is important to ensure that the most vulnerable people in all parts of the world are protected from the continued circulation of Covid-19 and other major diseases that continue to disproportionately affect the poorest.” Azra Ghani, Chair of Infectious Disease Epidemiology at Imperial College.
Among the study’s limitations, the authors acknowledge that the model is based on some necessary assumptions, including the precise proportions of which vaccine types were delivered, how they were delivered, and the precise timing of when new virus variants arrived in each country. They also note that the relationship between age and the proportion of Covid-19 deaths that occur among infected individuals is the same for each country.
“Ensuring fair access to vaccines is crucial, but it requires more than just donating vaccines. Are required improvements in vaccine distribution and infrastructure as well as coordinated efforts to combat vaccine misinformation and improve demand for vaccines . Only in this way can we guarantee that everyone has the opportunity to benefit from these technologies that save lives,” said Ghani.
Source: CNN Brasil
