Three U.S. senators from different parts of the country have tested positive for COVID-19.

Senators John Hickenlooper, Angus King, and Roger Wicker -- who are all fully immunized against the virus -- tested positive for the disease Thursday after experiencing symptoms.

In a statement, King said he started feeling "mildly feverish" Wednesday and tested positive despite all his efforts to adhere to public health protocols since the pandemic broke out.

Wicker also said he tested for the virus after experiencing mild symptoms but is "in good health."

The announcement from Wicker came as his hometown state of Mississippi has broken previous records for new infections this week. Mississippi is now reporting more new COVID-19 cases than any other state in the U.S.

On Twitter, Hickenlooper said he was experiencing limited symptoms and thanked the scientists who had labored hard to develop the vaccine.

The Centers for Disease Control and Prevention (CDC) said it had been expected there would be a "small percentage of fully inoculated individuals who still get ill, are hospitalized, or die from the virus.

However, the CDC said such cases are rare, noting there is evidence that getting inoculated may make the illness less severe for people who received the vaccine and still get sick,

The three senators are among the 71 members of Congress to get the virus since the start of 2020, the non-partisan group GovTrack said.

The three positive test results came as the Biden administration accelerates efforts to encourage Americans to receive booster shots beginning September in the wake of a growing pool of information that shows vaccine protections wane over time.

The U.S. Senate is in recess this week after it adjourned Wednesday, leaving it unclear whether any of the lawmakers had been in recent contact with other legislators.

The Senate will resume its session on September 13.

Earlier this month, Sen. Lindsey Graham said he had a case of COVID-19, although like King, he pointed out at the time the importance of having been fully inoculated.

More than 140,000 new infections and 821 fatalities were reported in the U.S. Tuesday, the CDC said.