From Halopedia, the Halo wiki
The Covenant arrived at the planet in 2549, leading to the Siege of Paris IV. A major engagement of the Human-Covenant War, the siege ended with the planet's glassing. According to his medical record, Staff Sergeant Avery Johnson received a heavy dose of radiation from a case of Covenant plasma grenades during the defense of the planet, causing him to contract Boren's Syndrome.
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