This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

MEMPHIS, Tenn. — Out of 635,000 people vaccinated in Mississippi, the state’s Department of Health says 78 have come down with COVID-19. That’s a rate of about one-hundredth of a percent.

“This low rate of breakthrough cases demonstrates how effective vaccines against COVID-19 have been,” state officials said.

“We knew we’d see some because it’s not 100 percent effective at preventing illness so it’s been fortunately an uncommon thing,” Mississippi Health Officer Thomas Dobbs said.

In Memphis, Dr. Steve Threlkeld said he had treated some cases of people who came down with COVID-19 after being fully vaccinated, referred to as “breakthrough cases.”

“We’ve seen a few,” Threlkeld said.

Threlkeld couldn’t give an exact number but said less than five of them have ended up in the hospital.

The Shelby County Health Department confirmed there were 21 COVID-19 breakthrough cases in Shelby County.

“The good news is essentially none of those people are dying,” he said. “What the vaccine does is dramatically shift the clinical spectrum of the disease. You get people who might’ve died and you get a mild illness.”

In fact, in a study of vaccinated health care workers, he says risk numbers plummeted.

“The actual likelihood of someone getting symptomatically affected after getting fully vaccinated is more like half a percent,” he said.

But there are still unknowns about why it happens.

One theory: the vaccines are less effective against variants. That’s why doctors say masks and social distancing are still critical.

You are considered fully vaccinated two weeks after your last shot.