Schools in Auckland will remain closed after the school holidays finish at the end of this week.
Prime Minister Jacinda Ardern says the advice about schools being able to reopen for term 4 was initial advice which has now changed.
"Today, the public health team have advised us that the state of the outbreak in Auckland has highlighted the need for robust safety measures to be in place before schools reopen."
School and early learning staff and support people who have contact with children and students will need to be fully vaccinated by 1 January, 2022.
Covid-19 Response and Education Minister Chris Hipkins told Checkpoint "there is a good chance" school will reopen for students in Auckland this year.
But he said nothing could be guaranteed with Delta.
A scenario where students do not return to school this year is a "worst-case scenario" he said.
Each week the government will assess its decision on reopening schools.
He said if schools go back before the end of year and teachers are not fully vaccinated, those staff will be tested for Covid-19 every week.
All teachers will need to be tested before returning to work, he said.
See how the day unfolded in the RNZ blog:
