The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused the current pandemic of COVID-19 and is highly infectious with relatively high mortality risk. In this study, we reviewed and summarized miscellaneous COVID-19 cases from vulnerable groups, including children and those with comorbidity, reinfections, coinfections and vaccinated individuals, and rapid transmission cases to understand if there are any specific SARS-CoV-2 variants that infect those groups. We concluded that there were no specific variants associated with higher rates of infection within certain groups, rather, they may tend to infect any groups with any immunity levels, regardless of geographical boundaries. A high prevalence of SARS-CoV-2 infection is mainly driven by the ability of viruses with genetic markers that have been associated with higher risks of transmission and immune escape in vulnerable groups. Disease severity is not only influenced by the virus, but also host conditions such as gender, age, comorbidity, and obesity. The likelihood of new emerging SARS-CoV-2 variants resulting from infections in vulnerable groups is high, thus monitoring viral genetic markers and mutations is crucial for outbreak preparedness. [ABSTRACT FROM AUTHOR]