Researchers at Covid-19 Modelling Aotearoa have used a mathematical model to figure out how rates of infection, hospital admissions, and deaths would change if our isolation requirements were scrapped.
The team found that ending the mandatory seven-day isolation period may cause a bump in infections in the first two months, with a 13-25% increase in the total number of Covid hospital admissions and deaths in the subsequent six months.
The modelling showed that after 4-6 months infections settled to a level that was only slightly higher than if mandatory isolation was maintained, but the additional infections were more likely to be in the vulnerable older population.
The SMC asked the authors to comment.
Dr Emily Harvey, Programme Co-lead, COVID-19 Modelling Aotearoa, comments:
“Staying home while infectious is one of the most important ways to keep your community safe from all infectious diseases. COVID-19 is a highly infectious disease, with potentially serious consequences, and even if the legal requirements around case isolation for COVID-19 are removed, staying home while sick (or while positive on a RAT even if not symptomatic) will remain key for protecting your community.
“Shifting from isolation requirements to ‘guidance’, especially if accompanied by the removal of the isolation support payments, will disproportionately impact those who are unable to stay home when sick, or who work in industries where their co-workers cannot.
“Additionally, all employers have an obligation to provide a safe work environment, and all schools have a responsibility to provide a safe classroom environment. 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.
“Case isolation reduces community transmission, and removing the case isolation requirements is expected to cause an increase in community transmission. However, because the policy changes under consideration and the behaviour change in response to any policy changes are not known, the magnitude of this increase is highly uncertain.
“COVID-19 Modelling Aotearoa has modelled three plausible transmission increase scenarios to investigate the impact of replacing mandatory case isolation with guidance.
“In all scenarios the modelling shows an increase in infections, hospital admissions, and deaths following the change in the short and longer terms. 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. The size of the bump will depend on how many people continue to follow guidance, what the guidance is, and how abrupt the change is. In the long term, the removal of case isolation is expected to lead to an increased ‘baseline’ level of infection, hospitalisations, and deaths, but this ‘baseline’ level is insensitive to the timing of the change.
“Although the modelling did not include consideration of the new bivalent boosters, we know these new boosters provide some protection against transmission and work well to restore protection against hospitalisation and death that will have waned since the last infection or vaccination. Having high uptake of these new bivalent COVID-19 boosters coming into winter will help to reduce infections, hospitalisations and deaths over the winter period.
“Coming into winter, we expect increased transmission of all respiratory illnesses, including COVID-19, influenza, and RSV. This is not considered in the modelling, but will have an impact on the capacity of the healthcare system to cope with any COVID-19 waves due to policy changes, behaviour changes, or new variants.
“Improving transmission reduction measures such as ventilation and filtration in businesses and schools, and widening sick leave eligibility and entitlements would help reduce the impact of all respiratory illnesses over winter.”
Conflict of interest statement: Dr Harvey’s employer receives funding from the MOH to provide modelling and analysis to govt officials on Aotearoa’s COVID response, and from the NZ Health Research Council for a project on modelling and equity for COVID-19 in Aotearoa.
Dr Dion O’Neale, Programme Co-Lead, COVID-19 Modelling Aotearoa, comments:
“Staying home when you’re sick has long been a key component of limiting the spread of infectious disease. This is especially true for airborne respiratory diseases like COVID-19. In Aotearoa this has recently taken the form of 7 days of mandatory isolation for confirmed COVID cases.
“Mandatory, fixed-length case isolation is a blunt tool for trying to reduce the number of people who are infectious in the community, but it does have the advantage that it applies equally to everyone. In contrast a move to “guidance only” risks leading to a situation where some people are able to stay home, while for others it may be more difficult to isolate due to factors such as their employment situation or lack of sick leave.
“In the absence of support for people who would otherwise find it difficult to isolate when sick, removing mandatory isolation requirements may push the burden of disease onto more vulnerable groups through increased transmission in their schools and workplaces, while having a smaller impact on those groups who are more easily able to follow the “stay home when you’re sick” advice.
“Quantifying the consequences of removing mandatory case isolation is difficult, in part because it is difficult to determine in advance how people’s behaviour will change in response to a policy change.
“At COVID-19 Modelling Aotearoa we have looked at the likely consequences of a sudden change is case isolation behaviour if mandatory isolation is no longer required. Our simulations suggest that we can expect a wave of increased infections, hospitalisations, and deaths in the couple of months immediately following the change, before returning to a level close to that expected in the absence of a policy change. Over the 6 months following removal of mandatory isolation we would expect to see an increase in hospital admissions and deaths of around 13%-25% although this range could be either higher or lower, depending on what follows removal of mandatory case isolation and which communications and support accompany such a change.
“While removing mandatory isolation requirements will lead to an increase in the expected number of infections and hospital admissions, it is possible that it will counterintuitively result in a reduction in the number of confirmed cases. This is due to expected reduced reporting rates and lower rates of testing once these are no longer linked to isolation requirements.
“Making sure that people are supported to stay home when sick is only one aspect of protecting people from respiratory diseases, like as COVID-19. Schools and workplaces have a duty to keep students and staff safe when they are on site. Making sure that ventilation and filtration systems are in place and are providing sufficient quantities of clean air is something that provides benefits in terms of keeping people healthy and reducing disease transmission, independent of case isolation requirements. Ventilation and filtration also plays an important role in reducing the amount of disruption from onwards transmission from asymptomatic infections which are estimated to be 30-40% for COVID-19.
“Independent of whether case isolation is mandated or only recommended, there are tools available that can limit the disruption due to case isolation. Previous work by COVID-19 Modelling Aotearoa estimated that around 15% of cases are still infectious at the end of a 7-day isolation period while an estimated 85% became non-infectious in less than 7 days.
“Rapid antigen tests (RATs) provide a great way of determining whether someone is still infectious. Using a test-to-release criteria for helping to inform people when it is safe to end their isolation can help to reduce both the number of hours infectious in the community and the number of hours of excess isolation. Test-to-release criteria are also useful for reducing transmission from people who might still be infectious even though their symptoms have reduced sufficiently for them to feel that they are able to return to work, or school.”
Conflict of interest statement: “I, along with others from COVID Modelling Aotearoa, am funded by the Ministry of Health to provide advice on the COVID response and from a Health Research Council grant to look at equity related to COVID in Aotearoa.”