COVID-19ワクチンは、最初の1年間で世界中で2,000万人の死亡を救いました

• の効果を決定する最初のモデリング研究[{” attribute=””>COVID-19 vaccines on a global scale estimates that 19.8 million out of a potential 31.4 million deaths were prevented in the first year after vaccines were introduced (December 8, 2020 – December 8, 2021).
• A further 599,300 deaths could have been averted if the World Health Organisation’s target of vaccinating 40% of the population in every country by the end of 2021 had been met.
• High- and upper-middle-income countries accounted for the greatest number of prevented deaths (12.2 million/ 19.8 million), highlighting inequalities in access to vaccines around the world.
• The study is based on data from 185 countries and territories and is the first to assess deaths averted directly and indirectly as a result of COVID-19 vaccination, using COVID-19 death records and total excess deaths from each country (or estimates where official data was not available). 

COVID-19 vaccines reduced the potential global death toll during the pandemic by more than half in the year following their implementation, according to estimates from a mathematical modeling study published on June 23, 2022, in The Lancet Infectious Diseases.

19.8 million out of a potential 31.4 million COVID-19 deaths were prevented worldwide in the first year of the vaccination program according to estimates based on excess deaths from 185 countries and territories.

The researchers estimate that a further 599,300 lives could have been saved if the World Health Organisation’s target of vaccinating 40% of the population in each country with two or more doses by the end of 2021 had been met.

Dr. Oliver Watson, lead author of the study, from Imperial College London, said: “Our findings offer the most complete assessment to date of the remarkable global impact that vaccination has had on the COVID-19 pandemic. 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). This initiative was set up because it was clear early on that global vaccine equity would be the only way out of the pandemic. Our findings show that millions of lives have likely been saved by making vaccines available to people everywhere, regardless of their wealth. However, more could have been done. If the targets set out by the WHO had been achieved, we estimate that roughly 1 in 5 of the estimated lives lost due to COVID-19 in low-income countries could have been prevented. ”

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%). The COVID-19 Vaccine Access initiative (COVAX) has facilitated access to affordable vaccines for lower-income countries to try to reduce inequalities, with an initial target of giving two vaccine doses to 20% of the population in countries covered by the commitment by the end of 2021. The World Health Organisation expanded this target by setting a global strategy to fully vaccinate 70% of the world’s population by mid-2022, with an interim target of vaccinating 40% of the population of all countries by the end of 2021.

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.

Several studies have sought to estimate the impact of vaccination on the course of the pandemic. These studies have focused on specific regions, such as individual countries, states, or cities. 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.

Mr. Gregory Barnsley, co-first author of the study, from Imperial College London, said: “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. It is also not possible to directly measure how many deaths would have occurred without vaccinations. Mathematical modeling offers a useful tool for assessing alternative scenarios, which we can’t directly observe 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 COVID-19 deaths occurring between 8 December 2020 and 8 December 2021. To account for the 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. Where official data was not available, the team used estimates of all-cause excess mortality. These analyses were compared with an alternative hypothetical scenario in which no vaccines were delivered.

The model accounted for variation in vaccination rates between countries, as well as differences in vaccine efficacy in each country based on the vaccine types known to have been predominately used in those areas. Notably, China was not included in the analysis owing to its large population and very strict lockdown measures, which would have skewed the findings.

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%. These findings do not account for the 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%.

More than three quarters (79%, 15.5 million/ 19.8 million) of deaths averted were due to the direct protection against severe symptoms provided by vaccination, leading to lower mortality rates. 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.

Vaccine impact changed over time and in different areas of the world as the pandemic progressed, the study found. 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.

Overall, the number of estimated deaths prevented per person was greatest in high-income countries, reflecting the earlier and wider rollout of vaccination campaigns in these areas (66 deaths prevented per 10,000 people in high-income countries vs 2.711 deaths prevented per 10,000 people in low-income countries). High- and upper-middle-income countries accounted for the greatest number of deaths averted (12.2 million/ 19.8 million), highlighting inequalities in access to vaccines around the world.

For the 83 countries included in the analysis that are covered by the COVAX commitment to affordable vaccines, an estimated 7.4 million deaths were averted out of a potential 17.9 million (41%). However, failure to meet the COVAX target of fully vaccinating 20% of the population in some countries is estimated to have resulted in an additional 156,900 deaths. Though this figure represents a small proportion of the total global deaths, these preventable deaths were concentrated in 31 African nations, where 132,700 deaths could have been averted if the target had been met.

Similarly, the shortfall in 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 the majority of these deaths (347,500/599,300 [59.7%]）。 地域的には、これらの死亡のほとんどはアフリカと東地中海の地域に集中していた（348,900 / 599,300）。 [58.2%] および126,800/599,300 [21.2%] 真っ直ぐ）。 すべての低所得国で40％の目標が達成された場合、これらの地域でのワクチン接種によって回避された死亡者数は2倍になります（現在のワクチン接種率で回避されたと推定される180,300人の死亡に加えて、さらに20万人の死亡が防止されました） 。

インペリアルカレッジロンドンの感染症疫学部長であるアズラガニ教授は次のように述べています。人々は保護されています。COVID-19の継続的な流行と、貧しい人々に不均衡に影響を及ぼし続けている別の主要な病気から世界で最も脆弱です。ワクチンへの公平なアクセスを確保することは重要ですが、ワクチンを寄付するだけでは不十分です。インフラストラクチャ、およびワクチンの誤った情報と戦い、ワクチンの需要を改善するための協調的な取り組み。そうして初めて、すべての人がこれらの命を救う技術から利益を得る機会を確実に得ることができます。」

著者は、彼らの発見に対するいくつかの制限に注意します。 特に、彼らのモデルは、提供されたワクチンの種類の正確な比率、それらがどのように提供されたか、各国での新しいウイルス変異体の到着の正確なタイミングなど、多くの必要な仮定に依存しています。 彼らはまた、年齢と感染者の間で発生するCOVID-19による死亡の割合との関係は、各国で同じであるとの仮説を立てました。 より広義には、COVID-19による死亡の国内レベルの報告の違いによる、エピデミックの真の死亡者数を計算する際の不確実性の文脈で、研究からの発見を考慮する必要があります。

リンクされたコメントで、研究に関与していなかったアリソン・ガルバニ教授は、[{” attribute=””>Yale University School of Public Health, USA, said: “The saving of more than 19 million lives by the unprecedented rapidity of development and roll-out of COVID-19 vaccines is an extraordinary global health feat. Nonetheless, millions of additional lives could be saved by more equitable distribution of vaccines.”

She added: “High coverage in an individual country not only benefits that country but contributes to worldwide reduction in transmission and emergence of novel variants. An enduring collective response is both pragmatic and ethically imperative.”

Reference: “Global impact of the first year of COVID-19 vaccination: a mathematical modelling study” by Oliver J Watson, PhD; Gregory Barnsley, MSc; Jaspreet Toor, PhD; Alexandra B Hogan, PhD; Peter Winskill, PhD and Prof Azra C Ghani, PhD, 23 June 2022, The Lancet Infectious Diseases.
DOI: 10.1016/S1473-3099(22)00320-6

The study was carried out by researchers at the Medical Research Council Centre for Global Infectious Disease Analysis at Imperial College London, UK. It was funded by a Schmidt Science Fellowship in partnership with the Rhodes Trust, World Health Organisation, UK Medical Research Council, Gavi, Bill and Melinda Gates Foundation, National Institute for Health Research and Community Jameel.