Health care personnel, first responders and other frontline workers across six states were tested weekly for COVID-19 over the course of 35 weeks, the CDC reported.
The agency reported that throughout the study, full vaccination against COVID-19 was 80 percent effective at preventing infection among the frontline workers "further affirming the highly protective benefit of full vaccination up to and through the most recent summer US COVID-19 pandemic waves."
The CDC also reported that prior to the predominance of the delta variant, the vaccine effectiveness point was at 91 percent. That declined to 66 percent once the delta variant became the predominant variant, the CDC said.
The CDC noted that this trend should be interpreted with caution because other factors, including time since vaccination along with "poor precision in estimates due to limited number of weeks of observation and few infections among participants."
"Although these interim findings suggest a moderate reduction in the effectiveness of COVID-19 vaccines in preventing infection, the sustained two thirds reduction in infection risk underscores the continued importance and benefits of COVID-19 vaccination," the researchers added.
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