By Ethan Covey
COVID-19 vaccination provides additional protection against hospitalization among people who have been previously infected with the SARS-CoV-2 virus (MMWR Morb Mortal Wkly Rep 2022;71:549-555).
“People who have had SARS-CoV-2 infection in the past have a degree of protective immunity, but it’s not perfect, and reinfections still occur,” said Ian D. Plumb, MBBS, a medical epidemiologist at the Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC.
“We assessed the benefit of getting a COVID-19 vaccine after a previous infection by looking at how well vaccination protected against hospitalization with a reinfection, including since the emergence of omicron.”
The study used data from Cosmos, an electronic health record (EHR)-aggregated data set, and looked at the vaccination status of 3,761 patients who tested positive for COVID-19 and had related hospitalization, compared with 7,522 matched control patients who had a negative test result.
The epidemiologists found vaccination offered strong protection against being hospitalized with a reinfection, and the highest level of protection was after a booster shot.
During the period of delta variant predominance (June 20-Dec. 18, 2021), the estimated vaccine effectiveness against COVID-19–associated hospitalization was 47.5% following two vaccine doses, and 57.8% following receipt of a booster.
During omicron predominance (Dec. 19, 2021-Feb. 24, 2022), the effectiveness was 34.6% following two vaccine doses and 67.6% after a booster dose.
“Since the emergence of omicron, we found that booster doses provided higher protection against being hospitalized with a reinfection compared with two doses,” Mr. Plumb said. “It’s going to be important to keep monitoring protection by vaccines after previous infection, and to understand more about the role of timing of previous infection and vaccination.
“Staying up-to-date with your vaccinations is the best way to protect yourself from severe COVID-19, even if you’ve had SARS-CoV-2 infection before,” he added.
