Entertainment reporter Catt Sadler warned people on Instagram on Tuesday not to “let your guard down” after she tested positive for the highly transmissible delta variant of COVID-19, despite being fully vaccinated.

Sadler said she contacted the virus while caring for an unvaccinated person she initially thought had the flu.

“I assumed I would be fine,” wrote Sadler, who said she wore a mask around the person. “Well, I’m not. I’m one of many breakthrough cases that we are seeing more of each and every day.”

Sadler said  her symptoms have included fatigue, two days of a fever, extreme congestion, and “even some weird puss coming out of my eye,” she revealed.

The pandemic “is very much NOT over,” said the former E! News co-host, who quit in 2017 after learning her male counterpart was earning double her salary.

The delta variant is now spreading across the United States, it is “relentless and highly contagious and grabbed ahold of me even after getting vaccinated,” she added.

“If you are vaccinated, don’t let your guard down,” Sadler warned. “If you’re in crowds or indoors in public I highly recommend taking the extra precaution of wearing a mask. I’m no MD but I’m here to remind you that the vaccine isn’t full proof.”

The Centers for Disease Control and Prevention notes on its website that so-called breakthrough infections in fully vaccinated people “are expected.”

“COVID-19 vaccines are effective and are a critical tool to bring the pandemic under control,” the CDC states. “However, no vaccines are 100% effective at preventing illness in vaccinated people. There will be a small percentage of fully vaccinated people who still get sick, are hospitalized, or die from COVID-19.”

More than 607,000 Americans have now died from COVID-19.

Amid a worrying slowdown in vaccination rates, the number of cases nationwide has doubled over the past three weeks to around 23,000 new infections each day.