New Zealand is experiencing its highest peak in Covid-19 cases since December 2022, professor Michael Baker says.

Last week, the ministry reported 6146 new cases of the virus and 19 further deaths.

That's a substantial increase on the number of cases reported the previous week - which stood at 3922.

The data came from wastewater testing, says Baker, but hospitalisations are also up.

"We're up to about 35 people a day going to hospital with this infection," he says.

Baker tells RNZ's First Up one in three people are still contagious five days after testing positive for the virus.

Despite the recommended isolation period now only being five days, Baker suggests people still getting a positive Covid-19 test wait to test again on day 6 or 7 before going back into society.

"The biology hasn't changed," Baker says, but there's more pressure for people to go back to work and school.

Baker says he would like to see money in this week's Budget going towards the Covid-19 response.

It's important for health and productivity that the government continues to fund booster shots, RAT tests and the anti-viral medication, he says.

Baker says it has to remain fair and equity has to be maintained.

Prioritising booster shots is also important, Baker says.

People over the age of 30 are eligible for a booster every six months.

-RNZ.