The Corrections Department found 499 new Covid-19 infections on Sunday, department director-general Ayut Sinthippan said.
The new cases come after the 460 imprisoned patients announced by the Centre for Covid-19 Situation Administration on Sunday, whose daily bulletins cover only the previous 24-hour period ending at midnight.
Of the 499 new infections, 292 were at Bang Khwang Central Prison; 91 at Khlong Prem Central Prison, 85 at Chachoengsao Central Prison, 20 at Thon Buri Remand Prison, nine at Chiang Mai Central Prison and two at the Central Special Treatment Centre.
Another 54 infected detainees had recovered, Mr Ayut said. .
The number of prisoners still under treatment as of Sunday was 14,784. They were being treated at 12 prisons and correctional facilities.
Mr Ayut said it was agreed at a recent meeting of the department's Covid-19 committee that all detainees must be inoculated as soon as possible.
Mass vaccinations would begin at prisons and detention centres where no infections had been detected. Jabs would follow at other facilities where Covid-19 had already been found, as the infected detainees must be first moved out for treatment, the department director-general said.
He said the administrators of all prisons and detention centres had been told to contact the department's Covid-19 committee if they needed any assistance.
Mr Ayut said since the establishment of the Covid-19 committee, the department had been able to collate and report the situation in prisons more systematically.
Members of the public are advised to follow the department's Covid situation reports published on its Facebook page or on Line ID@thaidoc, he added.