Covid-19 vaccination: Lifesaver with age-dependent effect

The consequences of the COVID-19 epidemic are still being felt. Coming to terms with them seems difficult, as opinions are entrenched and reliable data are difficult to collect. A recent publication provides a building block for a solid data basis with a comprehensive impact analysis of the global benefits of COVID-19 vaccination campaigns in terms of prevented deaths and years of life saved.

In the study, people over 60 accounted for 90 percent of the deaths prevented and 76 percent of the years of life saved. / © Getty Images/Luis Alvarez

The development and widespread introduction of COVID-19 vaccines is widely viewed by a large majority as a success of biomedical research and a guarantee for limiting the damage caused by the newly emerged coronavirus, which left the global population virtually defenseless. However, not everyone shares this view. Therefore, it is important to develop an idea of how many lives have been saved worldwide by COVID-19 vaccinations since their introduction.

Researchers led by Professor Dr. John PA Ioannidis from the Department of Medicine at Stanford University School of Medicine, USA, and colleagues are currently presenting a well-founded estimate in a publication published today in the research journal »JAMA Health Forum«.

The researchers analyzed the lives and years of life saved by vaccinated people worldwide since the first approval of vaccines in December 2020 until October 2024. This also includes data from the omicron period, which is missing in many other studies.

The number of deaths that might have occurred without vaccination and the plausible mortality reductions from various vaccines were estimated, as concrete figures are often unavailable. This was done using publicly available data stratified by age, pre- and post-Omicron vaccination periods, pre- and post-infection vaccination, and long-term care facility location.

The researchers focused on a realistic assessment based on empirical data on infection fatality rate (IFR), vaccine effectiveness (VE), and the infection status of the vaccinated population. The analysis takes into account different age groups, locations (home-care patients versus nursing home residents), infection status before vaccination, and the temporal division into the pre-omicron and omicron periods.

Specifically, the authors constructed a counterfactual scenario without vaccination and, on this basis, estimated the number of prevented deaths as the product of population size, presumed probability of infection without vaccination, IFR, and VE. Years of life saved were additionally calculated taking into account the average life expectancy per age group and a modification factor f, which takes into account that many Covid-19 deceased had a reduced life expectancy.

The values used for IFR and VE are based on systematic reviews, meta-analyses, and observational data. For the omicron period, the IFR was assumed to be two-thirds lower than in the pre-omicron period. The VE was assumed to be 75 percent (pre-omicron) and 50 percent (omicron). A total of 13.64 billion vaccine doses were administered worldwide, which served as the reference for calculating the number needed to treat (NNT).