PROJECT SUMMARY 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 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 will not take the vaccine. To address this issue, we will have two groups of MWCCS participants: 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 are: Aim 1: To conduct a mixed-methods investigation of the prevalence, correlates, and nuances of COVID-19 vaccine hesitancy among MWCCS participants. Results will help understand the concerns of PWH and HUC populations regarding COVID-19 vaccines based on age, sex, race/ethnicity, and underlying comorbidity 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 compare with the incidence of infections in non- vaccinated individuals. 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.