Fewer people die from Covid in better vaccinated communities, a large US study published in the BMJ on Thursday has suggested.
The findings, based on data across 2,558 counties in 48 US states, indicate that counties with high vaccine coverage had a more than 80 per cent reduction in death rates compared with largely unvaccinated counties.
This large benefit complements the growing body of evidence indicating individual level benefits of Covid-19 vaccination. A linked editorial proposes that encouraging people to keep up to date with vaccination saves lives.
As of 11 April, 2022, more than 11 billion Covid-19 vaccine doses had been administered and the World Health Organisation’s target is to vaccinate 70 per cent of the planet’s population by mid-2022.
Researchers at the US Centres for Disease Control and Prevention set out to estimate how increasing coverage of vaccines affected Covid mortality and cases among populations.
Their findings are based on more than 30 million cases and more than 400,000 deaths linked to the virus across 258 counties, which were reported during the second year of the pandemic, between December 2020 and December 2021.
They measured effectiveness by comparing reported incidence and mortality rates in counties with very low (0-9%), low (10-39%), medium (40-69%), and high (70% or more) vaccination coverage, defined as the percentage of adults (aged 18 and over) who had received at least one dose of a Covid vaccine.
After taking account of potentially influential factors, the researchers found that increased vaccination coverage in counties was associated with reduced levels of Covid-related mortality and cases.
During the first half of 2021, when the Alpha variant of coronavirus was dominant, the Covid mortality rate was reduced by 60 per cent, 75 per cent and 81 per cent in counties with low, medium and high vaccination coverage, respectively, compared with counties that had low coverage.
The corresponding figures for the reduction in cases were 57 per cent, 70 per cent and 80 per cent.
Similar reductions in mortality were seen during the second half of 2021 when the Delta variant became dominant in the US, although with smaller effects on case levels.
The observational study did not seek to establish cause and the researchers say several limitations should be considered when interpreting the data. For example, additional markers of severe disease, such as hospital admissions, were not explored and they did not control for factors such as rules on wearing a face masks and physical distancing at the time, which may have affected results.
But they point out that results were similar after further analysis, suggesting that they withstand scrutiny.
This study adds to the evidence that vaccination can prevent infection and illness on a large scale, writes Prof Christopher Dye at the University of Oxford in a linked editorial.
“The findings of this study also make clear that many more lives could have been saved, and will be saved, by encouraging people to keep up to date with vaccination in the face of waning immunity and new coronavirus variants and by achieving even higher population coverage,” he says.
“How many lives is a matter for others to explore. Meanwhile, this new study is another confidence booster for Covid-19 vaccines."