Castro-Torres, Yaniré, et al. “COVID-19 Serological Study in Non-Infected Vaccinated Subjects: Differences Among Age, Sex, and Vaccine Brand”. Puerto Rico Health Sciences Journal, vol. 42, no. 3, Sept. 2023, pp. 203-6, https://prhsj.rcm.upr.edu/index.php/prhsj/article/view/3098.