Reports from Covid-19 Modelling Aotearoa
Our Covid-19 modelling influences policy decisions, so we make it publicly available as soon as we can. All of our published work is assessed by our fast and committed peer review team to enable a degree of scientific certainty within the parameters of rapid change.
This pair of reports were provided to the NZ Ministry of Health and the COVID-19 Modelling Government Steering Group on May 3rd, 2023 in response to a request on April 21st, 2023 for advice on the impact of changing case isolation policies.
This report presents advice delivered to the NZ Ministry of Health in December 2022. It was prepared in response to requests for modelling advice around how COVID-19 case numbers and hospitalisations might be affected by policy changes enacted at different dates in the future, as well as a new variant of concern becoming dominant in November.
Addendum: Assumption of perfect case isolation within the home when estimating the effect of a change in case isolation policy
This document presents the findings of sensitivity testing of a modelling assumption made in two previous documents that present advice given to the NZ Ministry of Health in August and September 2022:
Estimating the effect of changes in case isolation on the effective reproduction number of COVID-19 in Aotearoa: September 2022
This document collates results and advice given to the NZ Ministry of Health in September 2022 as part of a rapid response to requests for modelling advice on consequences of removing case isolation.
Estimating the effect of Covid Protection Framework policy scenarios on the effective reproduction number of COVID-19 in Aotearoa: August 2022
This document collates results and advice given to the NZ Ministry of Health in August 2022 as part of a rapid response to requests for modelling advice on the on consequences of changing policy settings for cases, contacts, and community context.
The spread of transmissible disease is known to be tightly correlated with population movements, so we wanted to develop a means by which to infer daily travel patterns and thereby predict which people were likely to come into contact with one another during the course of a normal working day.
We made use of aggregate spatio-temporal data collected by telecommunications networks. This data provides total counts of contactable cell phones in over 2000 small geographical regions per hour, and cannot reveal any personal information about individual users.
This work was largely completed while Aotearoa New Zealand was at lockdown levels 3 and 4 and mobility restrictions were in place.
This memo was provided to the NZ Ministry of Health on November 16th, 2022 in response to a request for rapid advice on November 15th, 2022. The memo presents results for specific scenarios of interest: case isolation of 7 days or 5 days with no test-to-release, and 5 days with test-to-release. The method and results used here are from a previously published, internally reviewed report.
Since July 2022, Covid-19 Modelling Aotearoa have been using a compartment-based ordinary differential equation (ODE) model to simulate the spread of Covid-19 in Aotearoa New Zealand.
This age-structured model includes waning of vaccine-derived and infection-derived immunity, immune evasion of new Omicron subvariants, age-dependent hospitalisation and death rates, and changes in transmission resulting from behavioural and policy changes. The model is calibrated to data on Covid-19 cases, hospitalisations and deaths using an approximate Bayesian computation (ABC) method.
The model has been periodically updated to reflect the changing transmission and immunity landscape in New Zealand.
COVID-19 Modelling Aotearoa used a mathematical model to investigate the potential impact of shifting from mandatory COVID-19 case isolation to case isolation guidance on the number of infections, hospital admissions, and deaths over the next 6 months. Irrespective...
The BA.5 Omicron sub-variant is able to spread more easily than the previously dominant BA.2 sub-variant due to its immune escape characteristics.
Modelling Aotearoa New Zealand’s COVID-19 Protection Framework and the transition away from the elimination strategy
Covid-19 Aotearoa developed an age-structured model for the Delta variant of SARS-CoV-2 including the effects of vaccination, case isolation, contact tracing, border controls and population-wide control measures. We use this model to investigate how epidemic trajectories may respond to different control strategies, and to explore trade-offs between restrictions in the community and restrictions at the border.
Using mechanistic model-based inference to understand and project epidemic dynamics with time-varying contact and vaccination rates
This model was developed as a policy advice tool for New Zealand’s 2021 outbreak of the Delta variant of SARS-CoV-2 and includes the effects of age structure, non-pharmaceutical interventions, and the ongoing vaccine rollout occurring during the time period studied.
Quantifying the impact of isolation period and the use of rapid antigen tests for confirmed COVID-19 cases
New modelling by Covid-19 Modelling Aotearoa suggests that testing with Rapid Antigen Tests before ending isolation for confirmed cases of Covid-19 would significantly decrease the risk of onward transmission, while allowing many people to isolate for shorter periods.
Modelling the dynamics of infection, waning of immunity and re-infection with the Omicron variant of SARS-CoV-2 in Aotearoa New Zealand
Waning of infection-derived immunity means people become increasingly susceptible to being re-infected with Covid-19 over time.
A model to assess the risk of Covid-19 infection among international travellers arriving in Aotearoa New Zealand.
A preliminary assessment of the potential impact of the Omicron variant of SARS-CoV-2 in Aotearoa New Zealand
A report showing the results of simulated outbreaks using a branching process model to assess the potential impact of Omicron in Aotearoa New Zealand.
Effect of vaccination, border testing, and quarantine requirements on the risk of Covid-19 in New Zealand
We use a stochastic branching process model to investigate the risk of border-related outbreaks of Covid-19 and strategies to mitigate this risk.
We use a branching process model to simulate the Auckland August 2021 outbreak through to early January 2022, including the effects of increasing vaccine coverage by age group and time.
Preliminary estimates of hospitalisation numbers for the August 2021 outbreak, assuming we stay in Alert Level 4
We use the contagion network model to project case numbers and thus hospital and critical care numbers for the current Auckland outbreak of August 2021, with current vaccination coverage.
We seek to explain and explore how changes to Alert Level restrictions may impact the network of interactions on which Covid-19 is spread.
Using the FluTracking survey data for 2021 up until the week ending 29 August 2021, we can estimate the weekly incidence (new onset) of Covid-19-like symptoms within different age groups and different parts of the country.
We use an individual-based, Aotearoa-specific Contagion Network Model to simulate the spread of Covid-19 in the community for an outbreak comparable to that detected on 17 August 2021.
Updated modelling exploring how high rates of vaccine coverage might reduce the health burden from Covid-19 if combined with moderate public health measures to reduce transmission of the virus.
This report details the methods used for calculating the estimated weekly incidence of Covid-19-like and influenza-like illness in Aotearoa New Zealand, using data from the FluTracking weekly survey.
Estimating underlying prevalence of COVID in the community upon detection of a case with no known link to the border
This report was delivered to the government Covid-19 steering group on November 13 2020, and this version of the report was compiled on September 17, 2021. We use contagion network simulations to model the spread of COVID from index cases compatible with the known...
Effect of COVID-19 variants with increased transmission rates on the effectiveness of Alert Level 3 and Alert Level 4 for eliminating a community outbreak
These two reports describe the impact of the new variant of COVID-19. They were initially sent to government on April 18 2021. The first report, describes how Alert Level 3 would cope with the new variant, while the briefer addendum report uses the same analysis but for Alert Level 4.
In the first weeks of the 2021 Auckland August Covid-19 outbreak, the contagion network team provided a number of reports to officials with estimates of the likely size of the outbreak and updates on the estimated effect of Alert Level interventions on curtailing spread.
We use a range of data sources and analytic approaches to estimate the number of movements between regions of Aotearoa and to give some estimates of the risk of transmission of Covid-19 to regions outside of Auckland, during the early stages of the August 2021 outbreak.
Two technical reports in which we consider the epidemic course for the August 2021 cluster following the shift to Alert Level 4 restrictions in New Zealand, using a stochastic branching process model.
Exploring Covid-19 transmission risk and vulnerability through the Aotearoa Co-incidence Network (ACN)
The Aotearoa Co-incidence Network (ACN) provides a highly insightful tool to explore the manner in which the regions of Aotearoa New Zealand are connected to each other through co-incidence of individuals at workplaces and schools.
Covid-19 network modelling trilogy: Elimination, Alert Level 2.5 and other non-pharmaceutical interventions
Three network modelling reports that explore policy settings and possible interventions to prepare for the emergence of Covid-19, whether Alert Level 2.5 can be effectively used for future outbreaks, and a large number of combinations of transmission reduction interventions.
We use a mathematical model to estimate the effect of Aotearoa New Zealand’s vaccine rollout on the potential spread and health impacts of Covid-19 and the implications for controlling border-related outbreaks.
Vaccination and testing of the border workforce for Covid-19 and risk of community outbreaks: A modelling study
We use a stochastic model of Covid-19 transmission and testing to investigate the effect that vaccination of border workers has on the risk of an outbreak in an unvaccinated community.
We describe the development of a stochastic mathematical model for the transmission and control of Covid-19 in New Zealand.
Our researchers model the effects of various different border policies and testing regimes for frontline border workers on Covid-19 reincursion risk.
We assess the importance of early implementation of interventions for controlling Covid-19.
Early career researchers provide a valuable contribution to the research ecosystem in Aotearoa New Zealand, but are particularly vulnerable to the fallout from the Covid-19 pandemic.
We compare the economic costs of containing Auckland’s August Covid-19 outbreak using Alert Level 3 to those that might have resulted from the use of Alert Level 4.
Our researchers simulate the re-emergence and spread of COVID-19 in July/early August 2020, using a network model of all ~5 million people in Aotearoa New Zealand.
This paper summarises the modelling advice provided to Cabinet during the August 2020 outbreak of Covid-19 in Auckland, as well as detailing the methods used to provide that advice.
Our researchers find that the current effective reproduction number for Covid-19 in Auckland and the likelihood of cases occurring in other regions remains uncertain.
We aim to estimate inequities in infection fatality rates (IFR) for Covid-19 in Aotearoa New Zealand by ethnicity.
Our research suggests that Covid-19 contact tracing digital tools such as smartphone apps need to be designed to work hand in hand with manual contact tracing.
Our researchers estimate the risk of community COVID-19 outbreak originating at the New Zealand border and provide some recommendations for managing future risk.
Our modeling shows that a high-quality, rapid contact tracing system, combined with strong support for people in quarantine or isolation, can be highly effective in reducing the spread of Covid-19.
Our researchers modelled various border control measures and scenarios to assess the risk of Covid-19 re-entering Aotearoa New Zealand from incoming international travellers.
Our researchers estimate there is a 95% probability that Covid-19 has been eliminated in Aotearoa New Zealand after 2-3 weeks with no new reported cases.
Our researchers use a stochastic model to simulate Covid-19 spread in Aotearoa New Zealand, and report an estimate for its effective reproduction number (Reff) before and after implementation of Alert Level 4.
Our researchers have developed a structured model to look at the spread of Covid-19 in different groups within the New Zealand population.
A new epidemic simulation app shows how powerful our actions are in taking control of Covid-19.
An analysis of interventions used around the world and their effect on the spread of Covid-19 in the context of Aotearoa New Zealand’s Alert Level system.
How equitable is our healthcare system? Our researchers and colleagues analysed available data to estimate Covid-19 infection fatality rates by ethnicity in Aotearoa New Zealand.
Our investigators model Covid-19 containment and elimination scenarios in Aotearoa New Zealand, as the country considers an exit from a four-week period of strong population-wide control measures.
Our researchers compared the effectiveness of various strategies on controlling the spread of Covid-19 in Aotearoa New Zealand.