By Sandra Rose  | 

Anna Moneymaker/Getty Images

President Joe Biden tested positive for Covid-19 again, he announced in a tweet on Saturday.

Biden tested positive for Covid-19 on Saturday, days after he tested negative twice for the virus.

Biden, 79, says he has no symptoms, and he said he has a "rebound" case which he claims occurs "with a small minority of folks."

"I've got no symptoms but I am going to isolate for the safety of everyone around me," the tweet said. "I'm still at work, and will be back on the road soon."

Biden was vaccinated and boosted 4 times prior to testing positive for COVID twice in one month.

According to health experts, people with suppressed immune systems are re-infected in so-called "breakthrough" cases.