A study published in Open JAMA Network by investigators from Providence, one of the largest health systems in the United States, and the University of Chicago, found that the level of protection conferred by prior symptomatic COVID-19 infection in unvaccinated individuals was on par with the level of protection provided by mRNA vaccines, with natural immunity providing a longer window of protection than mRNA vaccines. The study was conducted before the highly transmissible variant of omicron emerged in the United States.
We found that before the emergence of the omicron variant, natural immunity offered a similar degree of protection against COVID-19 infection as mRNA vaccination. That said, vaccination is a considerably safer way to acquire that immunity.”
Ari Robicsek, MD, director of medical analysis for Providence and lead study author
Led by a team of expert clinicians and scientists at the Providence Research Network, the study examined data from more than 100,000 patients tested for SARS-COV-2 at 1,300 care sites across the vast healthcare system of Providence Health between October 1, 2020 and November 1. 2021. Researchers observed that prior COVID-19 infection protected 85% against reinfection and 88% against hospitalization, with protection against reinfection lasting up to nine months after initial infection, in as far as they could study.
The Providence study, one of the largest of its kind, shows the importance of connecting researchers to large-scale healthcare data and the influence an interconnected healthcare system can have in understanding specific public health challenges. The study is unique not only in its scale, but also in its long follow-up period and the inclusion of only unvaccinated individuals with symptomatic COVID-19.
“These data are critical in helping us understand the strength and longevity of natural immunity and allow us to compare the effectiveness of prior infection with mRNA vaccines,” said Amy Compton-Phillips, MD, director Providence Clinic. “The findings provide new insight into the duration of protection after initial infection among the unvaccinated population and may have important implications for vaccination guidelines and public health policy.”