Newly released Omicron modelling shows New Zealand could see 200 to 800 hospitalisations per day during the Omicron outbreak.
The University of Auckland modelling was carried out before Omicron was detected in the community.
It paints a bleak picture with experts expecting the outbreak to be large and put hospitals under significant strain.
The modelling shows for an outbreak starting on February 1, 2022 with high booster uptake peak hospital admissions will range from 200 to 800 a day with peak demand for hospital beds from 800 to 3300, depending on transmission rates.
Omicron was first detected in the community on January 23, 2022 as a result the entire country was plunged into the red traffic light setting and the timeframe for accessing a booster vaccination was shortened. So far more than 1.5 million Kiwis have received their boosters.
But Dr Audrey Lustig warned the modelling shows hospitals will be under pressure even with high vaccination rates.
"Demand on hospitals and intensive care units remains high and would put significant strain on our hospital capacity."
The modelling looked at three different transmission rates low, medium and high with 90 and 70 percent booster rates.
Based on an outbreak starting on February 1 with low transmission rates and 90 percent of eligible people boosted, New Zealand can expect to see a total of 386,400 cases and 460 deaths from the outbreak.
In the same scenario but with booster rates of 70 percent, there would be a total of 447,000 cases and 560 deaths.
In a medium transmission scenario with 90 percent of eligible people boosted there would be a total of 626,000 cases and 840 deaths.
If the booster rate was lowered to 70 percent, case numbers would jump to 680,200 and deaths would reach 950.
For a high transmission outbreak where 90 percent of eligible people were boosted, New Zealand would see 857,900 cases and 1330 deaths.
If boosters were lowered to 70 percent with high transmission rates, cases would hit 895,600 with 1450 deaths.
Professor Michael Plank said the modelling highlights the importance of boosters to stop hospitals from becoming overwhelmed.
"It's hard to overstate how effective vaccines are in blunting the health impacts of COVID-19," Plank said. "The only reason we can even contemplate outbreaks totalling hundreds of thousands of cases now is that we have high vaccination rates, drastically reducing the risk of hospitalisation and death.
"For most people, if you're up to date with your vaccinations, the risk of getting severely ill with Omicron is very low. But Omicron still has the potential to overwhelm healthcare systems because of the sheer number of cases it can cause in a short space of time."
Lead author Dr Giorgia Vattiato says along with boosters, mask use and social distancing are crucial for managing the virus' spread.
"This will flatten the curve - meaning that demand on the healthcare system is spread over a longer period rather than coming all at the same time."
Professor Plank says the message from the modelling is clear:
"The more people get boosted, the fewer hospital beds will be taken with COVID-19 patients - it's that simple."
The modelling also raised concerns about waning immunity saying those who received their boosters first - such as frontline workers - will become more at risk as time passes.
"Outbreaks that occur after significant waning of immunity can result in a higher overall health burden compared to outbreaks that occur during peak immunity. Maintaining high immunity levels across all groups will be important for future vaccination strategies."
