The COVID-19 pandemic has resulted in the extensive utilization of genetic vaccines, such as mRNA and viral vector vaccines. Booster vaccinations have also been employed to further combat the ever-evolving coronavirus disease. It is obvious that compared to the general population, patients with pre-existing medical issues are more likely to experience severe coronavirus disease and its related mortality. Patients have been given priority worldwide for vaccination, both for main and booster shots, due to the associated heightened risk. Nonetheless, a great deal of doubt surrounds the effectiveness of the vaccine, the degree of humoral and cellular immune responses in these patients, the likelihood of vaccination-related adverse effects, and the fact that these patients were excluded from crucial clinical studies. A study on the efficacy of COVID-19 vaccination and the gradual decline of immunity was recently published. According to the study, immune function was poorer in those who had received the COVID-19 vaccination 8 months after receiving two doses than in those who had not. These results were particularly noticeable in older people and those with pre-existing medical issues. Hence, we have tried to highlight the importance as well as shortcomings of COVID-19 vaccination in pre-existing patients before the outbreak of the pandemic.