Covid-19 was the third leading cause of death in 2021 behind heart disease and cancer, according to data from CDC, and a study from the Kaiser Family Foundation (KFF) found a large portion of those deaths could have been prevented by vaccination.

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Covid-19 the third leading cause of death in 2021

According to provisional death data from CDC, 415,399 people died of Covid-19 in 2021, an increase of around 60,000 deaths compared with 2020. Deaths that listed Covid-19 as the sole cause or a contributing cause increased from 384,536 in 2020 to 460,513 in 2021.

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The only diseases that killed more people in 2021 than Covid-19 were heart disease—which killed 693,021 people—and cancer—which killed 604,553 people. The fourth leading cause of death in 2021 was unintentional injuries, which killed 219,487 people.

The impact of (a lack of) vaccinations

However, KFF's study found a large portion of Covid-19 deaths since June 2021 could have been prevented with a primary series of vaccinations.

For the study, researchers looked at Covid-19 deaths since June 2021 when vaccines were widely available to the public and subtracted Covid-19 deaths among vaccinated adults from each month. The researchers also excluded children from their analysis, as vaccines may not have been available to children or adult permission may have been required.

The researchers then calculated the share of Covid-19 deaths among unvaccinated people using CDC data on vaccination status in 25 jurisdictions and applied the calculation to all adult Covid-19 deaths. They also used CDC studies on vaccine effectiveness to estimate how many unvaccinated deaths would have still occurred even if the individual had been vaccinated.

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Since studies on vaccine effectiveness have changed over time, the researchers applied different vaccine effectiveness estimates to each month, ranging from 91% effectiveness from June 2021 to December 2021, and 79% effectiveness from January 2022 through March 2022.

Notably, the researchers did not estimate the potential effect of booster shots, only a primary series of vaccination.

The researchers found that around 234,000 Covid-19 deaths since June 2021 could have been prevented with a primary series of vaccination. Those preventable deaths represent 60% of all Covid-19 deaths since June 2021 and 24% of all Covid-19 deaths since the start of the pandemic.

According to the researchers, the findings not only show the importance of vaccination, but also have implications for vaccinated people, as an increasing number of Covid-19 death are among the vaccinated, especially in recent months during the omicron wave.

"COVID-19 vaccines continue to offer tremendous protection from COVID-19 death, and that protection is significantly enhanced with recommended booster shots," the researchers wrote. (Kimball, CNBC, 4/22; Shapero, Axios, 4/22; Monaco, MedPage Today, 4/22; Bettelheim, Axios, 4/22; Amin et al., KFF study, 4/21)