The odds of getting infected with the virus, which causes COVID-19, were 2.3 times higher among people who had been infected before when compared to those who were fully vaccinated, according to the new report.
They used Kentucky's National Electronic Disease Surveillance System to find COVID-19 cases and checked for people who got infected a second time between May 1 and June 30 of this year.
They also utilized the state's immunization registry to look for fully vaccinated persons.
Researchers ended up with two groups. The first group of 246 was called case-patients, who experienced a second COVID-19 infection. The second was a control group of 492 who did not.
Some of the case-patients were fully vaccinated but still got a second infection, according to researchers. Still, the percentage of those who went unvaccinated and got infected again was higher, they found.
"These data further indicate that COVID-19 vaccines offer better protection than natural immunity alone and that vaccines, even after prior infection, help prevent reinfections," the CDC said in a statement.
“This study shows you are twice as likely to get infected again if you are unvaccinated. Getting the vaccine is the best way to protect yourself and others around you, especially as the more contagious Delta variant spreads around the country," added Dr. Rochelle Walensky, the agency's director.
Some existing research tilts the opposite direction of the study's conclusions. Multiple studies have indicated that vaccination does not provide more protection than prior infection.
Dr. Jeffrey Klausner, clinical professor of preventive medicine at the University of Southern California’s Keck School of Medicine, conducted one of those studies.
Klausner told The Epoch Times in an email that he reviewed the new CDC study and found it lacking.
"My concern is that in the Kentucky study the people with prior infection who go on to get vaccinated are different than those who do not. People with prior infection who get vaccinated are more likely to take other precautions such as mask wearing, avoiding indoor crowded settings, and get tested more often than those who do not get vaccinated. Those who did not get vaccinated likely engage in higher risk activities, have more exposure, and are less likely to get tested," he said.
"The very brief report is incomplete without showing that the two groups were equal in terms of risk factors for repeat infection," he added.
Other studies indicate that even one vaccine dose boosts the immunity in people who got COVID-19 and recovered.
That "could free up availability of millions of additional doses," they said.
Dr. David Boulware, professor at the University of Minnesota's Department of Medicine, who wasn't involved in either study, told The Epoch Times via email that he recommends people who recover from COVID-19 get at least one vaccine dose to generate long-term memory immune cells. But they should wait at least three months—preferably over six months—to get the jab, because the natural immunity takes time to fade.