WASHINGTON,-- Lindsey Graham, a veteran US Republican Senator, said on Monday afternoon that he has tested positive for COVID-19 even after being fully vaccinated.

Graham is the first US senator known to test positive for the coronavirus in months, and the first known "breakthrough" case among vaccinated senators, according to a The Hill report.

The senator said he started having flu-like symptoms on Saturday night and went to the House physician on Monday morning. Hours later he was informed that he tested positive for the virus.

"I feel like I have a sinus infection and at present time I have mild symptoms," he tweeted, "I will be quarantining for ten days."

"I am very glad I was vaccinated because without vaccination I am certain I would not feel as well as I do now. My symptoms would be far worse," he added.

Local media said Graham showed up at the Capitol on Monday and briefly spoke to reporters.

Less than 1 percent of fully vaccinated people experience a breakthrough COVID-19 infection in the country, said a CNN report on Monday, citing a Kaiser Family Foundation analysis of official state data.

The latest data from the US Centers for Disease Control and Prevention showed that less than 0.004 percent of people who have been fully vaccinated experienced a breakthrough case resulting in hospitalization, and less than 0.001 percent have died from the disease.