McAllen said teachers verified the student was wearing a mask at all times.
"The district health board will then follow through and see if there were any close contacts outside of school hours.
"They are going through that process."
It was the best possible outcome at the current point in time, McAllen said.
"We just need to watch this space in terms of what else happens across the Whanganui region."
Via a letter to parents and an online statement on Thursday afternoon, Whanganui High School said the confirmed case had been at the school for one full day and a very short period of another day.
The health and wellbeing of the children, staff and community was "a top priority", the statement said.
"We've got really robust systems and processes, and I was in direct contact with the Ministry of Education Covid-19 response manager for Whanganui," McAllen said.
"I spoke with Patrick O'Connor, Whanganui's medical officer of health, about three times during the day as well."
Despite the number of Covid-19 cases in Whanganui central and Marton, now at 26 with one recovered, the Ministry of Health has not notified of any locations of interest in the region.
Three Air New Zealand flights between Palmerston North and Auckland on February 10, 11 and 14 have appeared as close contact locations of interest, depending on where people were seated on those flights.
More details can be found at the ministry's locations of interest website.
Under phase 2 of the Omicron outbreak, the focus has shifted to high-risk exposure locations and for cases to do their own contact tracing.
Phone-based interviews where required are carried out, household contacts are identified and tested, while cases are required to tell people they are in contact with, including employers if they have tested positive for Covid-19.
