Shahrekord University of Medical Sciences Epidemiology and Health System Journal 2980-7891 10 4 2023 12 29 Clinical Challenges of the COVID-19 Vaccines: Frequency of Serious Adverse Events After Immunization in Hospitalized Patients 175 179 10.34172/ehsj.25214 EN Hamed Delam https://orcid.org/0000-0003-2054-4892 Atefeh Ghadri https://orcid.org/0009-0003-6341-9829 Zahra Keshtkaran https://orcid.org/0000-0003-1723-704X Behzad Rezaei https://orcid.org/0000-0001-9189-8685 Sahar Akbarpoor https://orcid.org/0000-0003-3771-5037 Journal Article 10.34172/ehsj.25214 2023 07 15 2023 11 28 Background and aims: Today, the role of coronavirus disease 19 (COVID-19) vaccines in preventing the disease and reducing the severity of the disease is undeniable; however, there is a possibility of serious adverse events following immunization (sAEFI) that might be life-threatening. The present study was designed to identify the frequency of the most common sAEFI in hospitalized people after receiving the COVID-19 vaccine in the south of Iran. Methods: This cross-sectional study was conducted in 2022. In total, since the start of the COVID-19 vaccination program in the city of Larestan, in the south of Iran, a total of 68 sick people have been hospitalized due to complications caused by the vaccine. The research tool of the present study was a standard checklist called the sAEFI of the COVID-19 vaccine. Results: A total of 68 hospital cases were reviewed. The mean age of the individuals with sAEFI was 59.78±12.70 years, and 21 (56.8%) of them were females. Acute respiratory distress syndrome (ARDS) was the most common 24 (64.9%) sAEFI. Based on the results, 2 (5.4%) had acute coronary syndrome (ACS), 2 (5.4%) had Guillain-Barré syndrome, and 2 (5.4%) had a stroke. Conclusion: It can be mentioned that there is always a possibility of sAEFI, but its frequency in the general population is extremely rare. However, the most common sAEFIs included adverse drug reactions, stroke, and Guillain-Barré syndrome. The readiness of health care staff for early detection of possible sAEFI can be effective in reducing the severity of the sAEFI.