(Corrects to symptomatic infection from infection in paragraph 5)
By Manas Mishra
(Reuters) -COVID-19 infections in a Colorado county with a Delta variant surge this spring were more common among fully vaccinated people than in the state's other counties where it was circulating at lower levels, a U.S. Centers for Disease Control and Prevention study released on Friday showed.
The study also found that the Delta variant caused more severe illness. Cases, hospital intensive care unit admissions and deaths were higher in Mesa County, Colorado, than anywhere else in the state, it said.
The CDC recently said in a leaked report it believed the Delta variant was producing more severe illness among the unvaccinated than other versions of coronavirus, citing studies outside the United States.
In Mesa County, the proportion of Delta variant cases more than doubled from 43% for the week ending May 1 to 88% for the week ending June 5. The study looked at data from April 27 to June 6 in the county, which accounted for half of Delta variant cases in the state.
An estimated "crude efficacy" of COVID-19 vaccines against preventing symptomatic infection among the fully vaccinated people in Mesa County was 78%, versus 89% for other Colorado counties where the variant was less dominant.
The lower estimates may "lend support to previous findings that COVID-19 vaccines provide modestly lower protection against symptomatic infection with the Delta variant," the study found.
In another study also published on Friday, CDC data showed that a person infected with COVID-19 who was fully vaccinated is less likely to be reinfected than someone who has had the virus but is unvaccinated.
The analysis of 246 patients in Kentucky showed that state residents with previous COVID-19 infections who were unvaccinated had 2.34 times the odds of reinfection compared to those who were vaccinated and had been infected previously.
"If you have had COVID-19 before, please still get vaccinated," CDC Director Dr. Rochelle Walensky in a statement.