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Focus of Presentation Cohort study recruitment can be complex, often requiring extensive pre-screening to recruit sufficient numbers of exposed and unexposed participants. We discuss a prospective study of the impact of racism on adult health in New Zealand (NZ), with emphasis on propensity-score based sampling and recruitment methods accessing participants from a national survey (NZ Health Survey 2017/18, n = 12,530 eligible adults). Discussion will cover sampling design, response rate, and confounder balance in the final sample. Key empirical results will be summarised. Findings The NZHS provided a sampling frame with complete baseline exposure and covariate data, giving n = 2,099 exposed individuals (reported racial discrimination on NZHS). A propensity-score model (stratified by ethnicity) allowed invitation of unexposed individuals balanced on key sociodemographic confounders. Recruitment used postal invitations with telephone follow-up: individuals could respond by paper survey, online questionnaire or telephone interview. Response rate was 54%, with comparable rates in exposed/unexposed individuals, with key sociodemographic factors well-balanced by exposure status. Conclusions/Implications Racism is an important determinant of health inequity, with limited prospective research in New Zealand. Our approach enabled appropriate recruitment from a sampling frame with baseline exposure status (NZHS), including allowance for exposure variability by ethnicity. Propensity-score matching on baseline covariates allowed for balance on key confounders at invitation, with balance maintained in the final sample. Key messages Secondary sampling from large national surveys can provide efficient recruitment for prospective studies. We achieved a highly satisfactory response rate, and propensity-score based sampling substantially balanced confounders between exposed and unexposed groups, enhancing study validity. [ABSTRACT FROM AUTHOR]

We use a stochastic branching process model, structured by age and level of healthcare access, to look at the heterogeneous spread of COVID-19 within a population. We examine the effect of control scenarios targeted at particular groups, such as school closures or social distancing by older people. Although we currently lack detailed empirical data about contact and infection rates between age groups and groups with different levels of healthcare access within New Zealand, these scenarios illustrate how such evidence could be used to inform specific interventions. We find that an increase in the transmission rates among children from reopening schools is unlikely to significantly increase the number of cases, unless this is accompanied by a change in adult behaviour. We also find that there is a risk of undetected outbreaks occurring in communities that have low access to healthcare and that are socially isolated from more privileged communities. The greater the degree of inequity and extent of social segregation, the longer it will take before any outbreaks are detected. A well-established evidence for health inequities, particularly in accessing primary healthcare and testing, indicates that Māori and Pacific peoples are at a higher risk of undetected outbreaks in Aotearoa New Zealand. This highlights the importance of ensuring that community needs for access to healthcare, including early proactive testing, rapid contact tracing and the ability to isolate, are being met equitably. Finally, these scenarios illustrate how information concerning contact and infection rates across different demographic groups may be useful in informing specific policy interventions. [ABSTRACT FROM AUTHOR]