The COVID-19 pandemic has caused a health crisis worldwide; therefore, it is necessary to understand factors related to its prognosis. In this study, we hypothesized that SARS-CoV-2-derived antigens presented by MHC class I may correlate with mortality in COVID-19 because they induce adaptive immune responses. Antigen coverage at the national level was inferred using country-specific HLA allele frequencies and relative predictions of binding antigens. We performed regression analysis between antigen coverage and the death rate due to COVID-19 across countries and found a negative correlation. This negative correlation was corroborated in multiple regression analysis with known risk factors, such as the prevalence of underlying disease. Furthermore, we analyzed antigen coverage in accordance with SARS-CoV-2 domains and identified a significant negative correlation when it was derived from the spike domain, which is reported to be favorable for COVID-19 prognosis. Taken together, the results indicate that the antigen coverage of SARS-CoV-2 may act as a favorable factor when explaining COVID-19-induced mortality.