Large, real-world study finds COVID-19 vaccination more effective than natural immunity in protecting against all causes of death, hospitalization and emergency department visits

Significantly, the all-cause death and hospital admission rates for vaccinated individuals were 37 percent lower than the rates for those with natural immunity acquired from previous COVID infection. The rate of ED visits for all causes was 24 percent lower for vaccinated individuals than for the previously infected.

"This large population study of the entire state of Indiana should encourage individuals everywhere to get themselves and their children vaccinated and not rely on natural immunity. While the incidence of COVID infection was higher in vaccine recipients (6.7 percent) than in individuals previously infected (2.9 percent), the vaccine protected against severe disease while natural immunity did not confer the same benefit," said study corresponding author and Regenstrief Institute Vice President for Data and Analytics Shaun Grannis, M.D. "As vaccinated individuals were more likely to actually get COVID than those with natural immunity, the lower death rate of vaccine recipients who develop COVID appears to be due to vaccination and not to a tendency for risk-averse behaviors, such as mask-wearing, hand sanitizing and social distancing."

Data on pairs of vaccine recipients and individuals with prior infections, aged between 12 and 110 years, matched on age, sex, CDC-defined COVID risk scores and dates of initial exposure (to the vaccines or the virus itself) were compared. This information was extracted from the Indiana Network for Patient Care, one of the nation's largest health information exchanges. Death reports from the State of Indiana were also analyzed.

"This study has important public health implications as previous studies investigated COVID-specific ED visits, hospitalizations and mortality but didn't capture the non-COVID related ones," said study first author Regenstrief Institute Research Scientist Wanzhu Tu, Ph.D. "Our work confirms that mRNA vaccines have kept people out of the ED and the hospital as well as lowered the likelihood of death from any cause. And we saw this pattern in every age group."

The study concludes, "The significantly lower rates of all-cause ED visits, hospitalization and mortality in the vaccinated highlight the real-world benefits of vaccination. The data raises questions about the wisdom of reliance on natural immunity when safe and effective vaccines are available."

"SARS-CoV-2 infection, hospitalization and death in vaccinated and infected individuals in Indiana USA, November 2020 -- February 2022," is published in the American Journal of Public Health. In addition to Drs. Grannis and Tu, authors are Pengyue Zhang, PhD, IU School of Medicine; Anna Roberts, M.S. and Katie S. Allen, B.S., Regenstrief Institute; Jennifer Williams, MPH, formerly with Regenstrief Institute; and Peter Embi, former Regenstrief Institute president and CEO, currently at Vanderbilt University Medical Center.