Teaching epidemiology, particularly more advanced concepts such as vaccine efficacy and herd immunity, can be very challenging in science classes geared for non-science majors. Nevertheless, as became quite evident during the recent COVID-19 pandemic, a thorough understanding of such topics is highly important to all individuals due to its role in informing future decision-making related to public health. One method for easing comprehension of difficult science content is to employ hands-on activities that engage students in critical thinking while visually demonstrating difficult concepts. While introductory activities illustrating the spread of disease through unprotected populations already exist, those that model the more advanced topics of vaccination and herd immunity are limited. In addressing this gap, the present manuscript describes an activity that expands on prior exercises through the addition of common biological buffers (MOPS and HEPES) mimicking vaccination status. Further, detailed exploration of buffer concentrations and interaction conditions during the development of this activity underscores potential avenues for class discussion of real-world outcomes. This includes the concept that exposure to a pathogen does not invariably result in illness, and vaccination does not always guarantee immunity against infection. Overall, the resultant activity creates avenues to enrich student comprehension of epidemiology, providing valuable insights into disease transmission, effectiveness of vaccination, and the dynamics of herd immunity.