The overarching primary research question for the QoVax SET Mixed Dose 1 and 2 study is: In the Queensland community, do heterologous COVID-19 vaccine doses 1 and 2 compared with homologous doses 1 and 2, offer higher recall levels of spike IgG, spike IgA, neutralizing IgG, and cell mediated immunity at 4 months post dose 2. The QoVAX Mixed Dose 1 and 2 study will address these specific research questions;

1. What are the host intrinsic (HLA type, genetic traits, immunological T and B cell receptor repertoires) and extrinsic factors (socio-economic health determinants, environmental exposures e.g. smoking) associated with variation in immune outcomes following vaccination?
2. Do members of the community who identify as Aboriginal and/or Torres Strait and/or South Sea Islander, or as being from diverse ethnic backgrounds, show similar vaccine responses?
3. Do certain pre-existing health conditions (autoimmunity, cancer, immunodeficiency), and medication use effect response variation of primary immune outcome measures? Further research objectives are to investigate medium-term health outcomes of vaccinated research participants at 12 months following recruitment, to identify factors associated with i) safety outcomes, and ii) vaccine efficacy outcomes in the study cohort.