Introduction: Viruses, such as SARS-CoV-2, are airborne and transmitted mainly via droplets. This type of transmission is particularly significant for people remaining in common closed space. It is also crucial in the case of homeless people who remain periodically in shelters, considering that in this subpopulation it is often problematic to follow anti-epidemic hygiene measures. Aim: The aim of this work was the assessment of COVID-19 incidence in the Shelter for the Homeless named after Sabina Kusznierów in Olsztyn (Poland), and the analysis of the development of a micro-epidemic. Material and methods: Data were collected from the Shelter for the Homeless named after Sabina Kusznierów in Olsztyn. The retrospective analysis embracing the period of December 2020 and March 2021 was performed for 82 shelter residents. Attendance lists and personal identification numbers (PESEL) constituted the basis for obtaining the results of SARS-CoV-2 PCR tests from the gabinet.gov.pl portal. Results and discussion: Each of those residents remained overnight in the shelter at least once. In total, 50% of the analyzed individuals became infected. No cases of reinfection were noted. This work presents a case of COVID-19 transmission in closed space in which ‘patient zero’ appeared on December 18, 2020. Conclusions: The described epidemic demonstrates the classic scenario of an infectious disease transmission in closed space. Owing to the implications for society, ease of the infection transmission in the general population, and the lack of other real measures to influence this subpopulation, we believe that this group should be prioritized when planning vaccinations during possible subsequent waves of infections, if such should occur.