Between early-2020 and mid-2023 researchers in Covid-19 Modelling Aotearoa (CMA) compiled information from literature on a range of factors relevant to differential risk of COVID-19 transmission. This was complemented in places with analysis of data from Aotearoa New Zealand in order to contextualise international findings and to place them alongside information about the demographics of Aotearoa. This report provided context around factors that might affect the risk of infection but which were not necessarily (able to be) specifically addressed in mathematical modelling from CMA. Most of this information was collated mid to late 2021. After minor updates to this document at various points it received internal peer review September 2022 and has been revised following that feedback.
This report provides a literature review of the risk factors for COVID-19 infection, and discusses the implications for Aotearoa New Zealand (NZ). Grounded in a theoretical framework outlined by Cevik and colleagues (2021), we detail how risk of infection is influenced by factors such as the type of environment, the contact patterns of individuals, individual-level and socio-economic factors. Accounting for a vast range of international research undertaken in contexts where COVID-19 has been widespread, we outline factors impacting on transmission risk in NZ, and which populations are likely to be affected. We maintain an explicit focus on risk factors for Māori and Pasifika Peoples. Key findings include:
- Indoor settings carry higher transmission risk than outdoor settings, with this related to ventilation and crowding. Importantly, outdoor settings do still carry some risks, especially in colder weather.
- Public-facing roles, essential work, and shared-work environments all carry higher risk of infection. These roles are often lower paid, have less opportunity to work from home, and are disproportionately composed of workers from marginalised groups in other countries, and Māori and Pasifika Peoples in NZ.
- Different mitigation strategies explain why findings on risk in school environments are mixed. School-age children may carry lower risk of infection, but school re-openings have been shown to drive outbreaks, especially in cases where mitigation strategies are not followed such as mask-wearing.
- Infection risk is higher within households with many close contacts. Household crowding exacerbates risk, as does housing quality such as damp living conditions or indoor pollution. Marginalised groups in the US and UK are over-represented in crowded households of poorer build quality and Māori and Pacific peoples are also over-represented in these types of households in NZ.
- Individuals who are older and/or have comorbid health conditions have increased infection risk. In the NZ context, Māori and Pacific peoples have higher rates of co-and-multi-morbidity.
- Across each of the risk factors considered within the model of risk proposed by Cevik and colleagues such as environment, contact patterns, individual and socioeconomic status, Māori and Pacific peoples face heightened and compounded risk. Mitigation strategies must be tailored towards these populations to achieve equitable public health outcomes.
- There are some caveats and limitations that should be considered with our review. Pathogen characteristics are out of scope for this review (which may be particularly important to consider when multiple variants of the same infectious disease emerge), and the review cannot be considered systematic. Despite this, the review does provide an extensive summary of risk factors for COVID-19 infection in NZ.