A leading scientist estimates Covid-19 cases could be more than twice the number that show up in official figures.

In the latest weekly update, 20,522 new cases of people who tested postive for Covid-19 were reported for the week ending 30 October.

New Zealand Institute of Medical Laboratory Science president Terry Taylor told First Up the number of cases in the community was likely to be significantly higher.

"If we look at the wastewater results at the moment ... ultimately that's all we've got to go by, we're probably looking more like about 50,000 [cases] a week."

The Ministry of Health has said analysis of wastewater testing, a key measure of infection in the community, indicated reported cases may be 35 percent to 45 percent lower than the actual number.

Institute of Environmental Science and Research molecular biologist Dr Brent Gilpin has said there are more cases than those being reported, and Omicron remained the dominant strain.

With predictions of a Covid-19 wave, Taylor said he would be masking up, and encouraged others to think of the vulnerable.

"I think we often just think of ourselves, but there's people that haven't had Covid yet, that if they do get it are at a huge risk of more than likely having an adverse outcome, in other words, dying. It's not always just about us."

New Zealand Institute of Medical Laboratory Science president Terry Taylor 

Taylor said more than 250 scientists and technicians had been lost to the pathology sector industry in the last twelve months.

"We're no different than any other health sectors.

"Work conditions have deteriorated because of the load of the work that's been coming in and the stress.

"We're an older scientist workforce as well, which makes it difficult. It takes at least five years to train scientists, so it's not going to be a quick fix either.

"Realistically we should have had plans in place in the past, but we're certainly working on it all right now."

Having one organisation, Te Whatu Ora, now dealing with this makes things easier, he said. "We're going to get there eventually, but in the short term it's going to be quite difficult for us to get through things."

He emphasised that while laboratory blood tests had been slowed down by the backlog and staff shortage issues, accuracy was not being compromised. More than 200,000 tests were carried out daily across the country's laboratories.

"I just want to reassure the public the only thing that really will happen in this situation is that the times will stretch out. It's not that we're going to make mistakes, we'll certainly still keep our quality going.

"For our diagnostic services, we are always going to be the bottleneck because clearly with the biopsies being passed through our pathologists and scientists and on to the appropriate consultants, it's a timing thing, and we just do not have enough at the moment."