The objective of this study is to document SARS-COV-2 infection and immunity and related determinants, as well as to examine how measures to stop or slow the spread of SARS-CoV-2 (e.g., physical distancing, personal hygiene, quarantine, travel restrictions) are received, understood, and being taken up by gay and bisexual men (GBM). The aims are: 1. Biomedical: * Ascertain occurrence of COVID-19 by documenting SARS-CoV-2 immunity within both HIV-positive and -negative participants across three jurisdictional sites. * Identify risk factors for COVID-19 acquisition, including sociodemographic and socioeconomic characteristics (e.g., site of recruitment, ethno-cultural identity, type of employment, financial strain), behaviours (e.g., adherence to physical distancing, sexual relations), and potential exposure to COVID-19 (e.g., national or international travel, close contact with a confirmed COVID-19 case). * Characterize the clinical syndrome and related severity of both diagnosed cases and those having demonstrable immunity, while considering HIV status and clinical factors (e.g., comorbidities including level of HIV-related immune deficiency, hypertension, diabetes). 2. Behavioural & psychosocial: * Assess the understanding of COVID-19 mitigation strategies (e.g., physical distancing, quarantine, hygiene, travel restrictions) among GBM, sources of COVID-19 information, if and how these mitigation strategies were applied by GBM, and barriers to practicing these prevention behaviours. * Explore the direct and indirect impacts of the pandemic on GBM, including how COVID-19 is impacting mental health outcomes, experiences of loneliness, sexual behaviours, substance use patterns, and access to essential healthcare and services (e.g., potential disrupted access to HIV/STI testing, treatment, and prevention (e.g., PrEP), mental health services, harm reduction services). * Provide an integrated approach to knowledge translation (KT), including adapting behavioural HIV prevention interventions based on our findings to reduce COVID-19 transmission behaviours.