Arorangi prison, on Rarotonga, has experienced an outbreak of Covid-19.
Cook Islands Prime Minister Mark Brown reported that "several prisoners and prison staff" have tested positive for the Omicron variant.
Mr Brown said that the cases at the prison were "not unexpected" and Te Marae Ora Health Ministry had a special plan in place to manage them.
He added that all the inmates and wardens are fully vaccinated and protected, and wished them a rapid recovery.
There are now 359 active cases of Covid-19 in Cook Islands.
In a national address Mr Brown reported that there have been a total of 835 Covid-19 cases since the outbreak began last month. Rarotonga has experienced 831 cases while Aitutaki has reported 4; with 476 people recovered.
He also passed on a special meitaki ma'ata to all the teachers across the country who have supported home-schooling as well as keeping schools open.
Mr Brown emphasised that the public health measures in place make schools a safe place for both students and staff, despite the spread of Omicron in the community.