A COVID-19 vaccine shot offers solid protection against hospitalization caused by reinfection with the SARS-CoV-2 virus, according to new data from the Centers for Disease Control and Prevention. A booster provides even more of a safeguard, the agency found.
Agency investigators used electronic health record data to determine the vaccination status of more than 3,700 patients. All had positive SARS-CoV-2 results from a nucleic acid amplification test associated with hospitalization. The results were then compared with those from a matched control group.
During the omicron-dominant period of the pandemic, initial series vaccine effectiveness was 35% against reinfection leading to hospitalization, they found. Efficacy then rose to 68% after a booster dose. A booster dose was protective even when the study participant’s previous infection occurred after receiving a second initial vaccine dose.
Omicron ups risk of reinfection
The findings provide important data to consider as the proportion of the U.S. population with SARS-CoV-2 infection increases, the investigators wrote. Many previously infected people could be at risk for reinfection with severe illness, they said. In the current study, about 50% of reinfections occurred while omicron was predominant, they noted.
Notably, the efficacy of the initial two vaccine doses declined from approximately 60% during the delta-predominant period of the pandemic, to about 35% during the omicron-predominant period, they said.
“To prevent COVID-19–associated hospitalization, all eligible persons should stay up to date with vaccination, including those with previous SARS-CoV-2 infection,” they concluded.
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