Sen. Tim Kaine (D-Va.) said on Thursday that he and his wife tested positive for COVID-19 antibodies, an indication that they have previously been infected with the disease. 

“We each tested positive for coronavirus antibodies this month. While those antibodies could make us less likely to be re-infected or infect others, there is still too much uncertainty over what protection antibodies may actually provide. So we will keep following CDC guidelines," Kaine said in a statement. 

Antibody tests, also known as serologic tests, determine whether someone has been infected and has built up some an immune response to the virus. They are different from diagnostic tests that determine whether someone currently has the disease. 

The disclosure makes Kaine the first senator known to have coronavirus antibodies that has not previously announced they had the disease.

Sen. Rand Paul (R-Ky.) is the only senator known to have been tested positive for the coronavirus, though several have had to quarantine after exposure to an infected individual. 

Kaine said in his statement that he tested positive for the flu earlier this year and received treatment for that through mid-March. 

At the end of March he had new symptoms that he said he initially tied to the flu and seasonal allergies. His wife, Anne, also was sick with symptoms linked to the coronavirus, including a cough and fever, but they did not get tested at the time. 

“We each talked to our health providers in early April and they thought it possible that we had mild cases of coronavirus. We were both at home in Richmond, working remotely and isolated from others," he said. 

"Due to the national testing shortage, we were not tested for the virus but continued isolating and watched for any worsening of symptoms. By mid-April we were symptom free," he added. 

The Centers for Disease Control and Prevention (CDC) issued new guidance this week raising concerns about the accuracy of the tests and noting that while someone might have antibodies indicating that they've had the virus, it's not clear how long immunity from catching the disease for a second time would last. 

"Until the durability and duration of immunity is established, it cannot be assumed that individuals with truly positive antibody test results are protected from future infection," the CDC wrote.