Hospitalisations and deaths could rise by between 13 to 25 per cent over six months if the Government ends mandatory isolation for Covid cases, new modelling shows.

After an initial rise in infections in the first 1-2 months, the level of transmission was likely to settle after 4-6 months to a level slightly higher than if mandatory isolation rules were maintained, the modelling showed.

Cabinet is today discussing whether to relax Covid restrictions which legally require anyone who tests positive for Covid to self-isolate for seven days. An announcement is expected this week.

A report by Covid-19 Modelling Aotearoa, published this afternoon, estimated the potential effect of relaxing the isolation rules.

 “What the modelling shows is that removing isolation requirements would potentially lead to a short-term wave in cases and downstream effects - hospitalisations and deaths,” said Professor Michael Plank, one of the co-authors of the report.

“But then that wave does come back down again. In the long-term, the difference in infection levels versus if we keep those isolation requirements is relatively small.”

Professor Plank stressed that there was significant uncertainty about the exact impact of ending mandatory isolation.

“It’s very difficult to know what the effect will be because it really depends on peoples’ behaviour. And of course, even if the legal requirements are removed it is not a good idea to be out and about when you’re sick.

 “It’s really important for people whether you have Covid or flu or whatever just to stay home when you’re sick.”

Covid-19 modeller Professor Michael Plank said relaxing mandatory isolation would lead to an initial wave of infections in the first 1-2 months, which would then settle after 4-6 months. Photo / Supplied

To account for this uncertainty, Covid-19 Modelling Aotearoa ran three alternative model scenarios which took into account potential differences in people’s responses to new isolation rules.

“In all scenarios the modelling shows an increase in infections, hospital admissions, and deaths following the change in the short and longer terms,” said Dr Emily Harvey, one of the co-authors of the study.

“In particular, the increase in transmission causes a ‘bump’ in the 1-2 months after the change, with the biggest impacts being on those who are older and those who have been shielding and have avoided infection so far.”

If people continued to test and isolate voluntarily, the increase in hospital admissions and deaths could be as low as 6 per cent. That would equate to 81,000 more Covid cases over a six-month period, along with 700 more hospital admissions and 73 more deaths.

In the worst-case scenario, in which many people left their homes while infectious, the rise in hospital admissions and death could be higher than 35 per cent - around 2100 extra hospitalisations and 225 more deaths over six months. So far, the Covid-19 death toll in New Zealand is around 2700.

Under the most likely scenario, transmission would increase by around 10 per cent after the isolation rules were relaxed, the report said. This would lead to an increase of around 140 more hospital admissions and seven deaths a week for the first 1 to 2 months after the rules changed.

If isolation rules are relaxed, the exact level of Covid transmission will be influenced by any guidance Government provides. Encouraging voluntary test-to-release (in which people can end isolation after a negative test) could reduce transmission. On the other hand, advising people to only isolate while symptomatic could increase the risk of widespread transmission.

The Covid-19 Modelling Aotearoa report also noted other factors that could shift outcomes towards the lower transmission scenario. Those factors could include strong, clear public health messaging on the importance of following isolation guidelines, availability of and access to rapid antigen tests and financial support for people to isolate.

Dr Harvey said that shifting from isolation requirements to “guidance”, especially if accompanied by the removal of isolation support payments, would disproportionately affect people who were unable to stay home when sick.

”Additionally, all employers have an obligation to provide a safe work environment and all schools have a responsibility to provide a safe classroom environment,” she said. “If there are no legal Covid-19 case isolation requirements, and no legal masking and ventilation (clean air) requirements related to Covid-19, schools and businesses will be required to develop their own rules to keep staff and students safe. Hopefully MOH, MBIE and MOE are working to prepare guidance to support businesses and schools.”

The modelling was provided to the Ministry of Health in late March and would be part of the data which ministers will use to make their decision this week.

Health Minister Ayesha Verrall said last week that the Government would weigh up the latest public health advice as well as the state of the health system heading into winter.

Most overseas jurisdictions have already scrapped mandatory isolation requirements.

Over the most recent reporting week, the Ministry of Health recorded another 275 hospitalisations and 16 deaths of people with Covid-19, bringing New Zealand’s cumulative toll to 2687.

With more than 300 deaths already reported in 2023, experts expect Covid-19 to claim twice as many lives this year as those typically attributed to influenza, which averages about 500.