(HealthDay News) — Unvaccinated individuals with prior symptomatic COVID-19 have a much lower risk for acquiring recurrent COVID-19 than unvaccinated individuals without prior COVID-19 for up to nine months from the index infection, according to a research letter published online April 20 in JAMA Network Open.
Jessica P. Ridgway, M.D., from the University of Chicago, and colleagues assessed the degree and duration of protection associated with natural COVID-19 immunity in unvaccinated individuals.
The analysis included data from unvaccinated patients with COVID-19 symptoms tested for severe acute respiratory syndrome coronavirus 2 at 1,300 sites in the Providence Health Care System (six states) between Oct. 1, 2020, and Nov. 21, 2021 (24,043 cases [positive initial test] and 97,572 controls [negative initial test]).
The researchers found that 2.8 percent of controls and 0.4 percent of cases developed COVID-19. Among cases, prior COVID-19 was associated with protection of 85 percent against any recurrent COVID-19, 88 percent against hospitalization for COVID-19, and 83 percent against COVID-19 not requiring hospitalization. For up to nine months from initial infection, protection remained stable.
“mRNA vaccines are associated with similar prolonged protection from severe COVID-19 as found in our study, although vaccine-associated protection from mild COVID-19 has been shown to wane at six months,” the authors write.