ABSTRACT MWCCS participants are a high-risk group for severe COVID-19 disease in terms of being HIV- infected, predominately of elderly age, and having numerous underlying comorbidities. Therefore, it is imperative for their health that they be vaccinated with the new COVID-19 vaccines. To date, however, there are only anecdotal data on COVID-19 vaccine acceptance and efficacy in people with HIV (PWH). The MWCCS is ideal for analyzing (a) the acceptancy and effects of COVID-19 vaccine(s) in male and female PWH and matched HIV-uninfected controls (HUC), (b) the impact of age and co-morbidities on vaccine immune response and protection against COVID-19, and (c) the social, economic, and behavioral changes after COVID-19 immunization as compared to the individuals who opted to not take the vaccine. To address this issue, we will have 2 groups of MWCCS participants in this study: Group A: Male and female PWH and HUC who choose to receive a COVID-19 vaccine, Group B: Male and female PWH and HUC who choose NOT to receive a COVID-19 vaccine. The aims of our proposed longitudinal observational study for this OAR Innovation application are: Aim 1: To conduct an MWCCS-wide, mixed- methods investigation of the prevalence, correlates, and nuances of COVID-19 vaccine hesitancy among MWCCS participants. Results will help better understand the concerns of PWH and HUC populations regarding COVID-19 vaccines based on age, sex, race/ethnicity, and underlying comormidity burden. Aim 2: To determine the incidence of natural SARS-CoV-2 infections post- COVID-19 immunization in PWH as compared to HUC of the same age, sex, and ethnicity/race and also compare with the incidence of infections in non-vaccinated individuals. Because of budgetary limitations in the OAR Innovation Fund supplement, we will restrict Aim 2 to obtaining one specimen at baseline, just prior vaccination in Group A, and within comparable time periods for Group B. Subsequent samples collected during the core MWCCS visits will be used in the serological analyzes. These samples will allow us to determine the serological COVID-19 status pre-immunization, and post-immunization seroconversions for S and N proteins. The titration of anti-S responses post immunization will indicate vaccine immune response, while anti- N antibody titers will indicate natural SARS-CoV-2 infection This information will allow the identification of asymptomatic and symptomatic individuals infected with SARS- CoV-2 post- vaccination and in non-vaccinated group. The if these infections in the MWCCS will allow a targeted use of core samples in depth investigation of the immune mechanisms of vaccine- mediated protection, the immunologic responses and virologic characteristics of breakthrough SARS-CoV-2 infections, and the impact of the vaccination on underlying HIV infection. Importantly, timely funding from this OAR Innovation opportunity is critical to our addressing these aims prior to the broad rollout of the COVID-19 vaccines to our PWH participants. We are in a race to obtain this critical information and specimens prior to the wide availability of current FDA EUA vaccines to our MWCCS participants. The MWCCS clinical research sites across the United States and the data center are ready to launch this new study as soon as funding is available and we receive sIRB approval.