Covid-19 testing advice needs to be broadened to get a better understanding of the infection rate, which could be much higher, a modeller says.
Covid-19 Modelling Aotearoa project leader Dion O'Neale told Morning Report it was hard to tell what the real infection numbers could be, due to changes in the system like to testing requirements.
"Why it's important to know those infection numbers better is because ... that gives us a better leading indicator on how many people we are going to see turning up in hospital.
"So if we wait for those people to turn up in the hospital and use hospitalisations or ICU admissions as our indicator of how things are tracking, by the time those get to a bad number, it's going to be too late, you don't get to step back from there."
Data from New Zealand and overseas showed that while it was younger people getting infected initially in outbreaks, meaning there was low hospitalisation rates, that usually seeped into the older age group later in the outbreak, which is likely to result in more hospitalisations, O'Neale said.
"Eventually when those infections do catch up, you see higher hospitalisation rates per infection come through. So using current hospitalisation rates as a predictor for what's going to happen in future can be dangerous."
But a "good quality infection prevalence survey", broadening of testing advice, and asking people to upload both negative and positive rapid antigen test results would help to understand New Zealand's infection rate, he said.
"We need to know about those negative RAT results to know what that rate is. So not just the absolute number of cases.
"But the other thing that would help is some slightly broader requirements or broader encouragement for people to go and get those RATs in the first place.
"So at the moment there's this advice being given out saying only seek a test if you are symptomatic. Well we know with Omicron and particularly for their vaccinated individuals, lots of people are going to be asymptomatic or have very mild symptoms, so they might not even know that they are infected.
"But if those people know that they have been the contact of a confirmed case ... basically through any context other than being a direct household contact, we'd like them to be going and getting a test as well."