Background: The COVID-19 pandemic is one of the worst pandemics of recent times. Getting vaccinated against COVID-19 is a preventative strategy that helps in the prevention of the infection and reduces its severity. This study aimed to measure the reinfection and vaccination rates among COVID-19 patients who were admitted to Ain Shams University (ASU) Hospitals during the pre-vaccination era (April 2020–March 2021) and correlate their vaccination status with the incidence and severity of the reinfection. Methods: A retrospective cohort study was conducted that includes patients diagnosed with SARS-CoV-2 infection and admitted to ASU Hospitals during the pre-vaccination era. Data about the first COVID-19 infection were extracted from the patient's records and then a random sample of patients was selected and data about vaccination and re-infection rates were collected from them through an interview questionnaire. Results: 340 out of the 400 included subjects received COVID-19 vaccination (85%); 4.41% received incomplete doses; 67.06% received full vaccination; and 28.23% received full vaccination with an additional booster dose. 53.61% of booster vaccinations used the same vaccine each time, while 46.39% received different vaccines. Regarding the reinfection rate, it was higher among the unvaccinated group compared to the vaccinated (20% versus 13.82%) but this difference was not statistically significant. Also, the length of stay in hospital during the reinfection was 6 days in both groups.   Conclusion:  Although our results revealed no statistically significant difference between the vaccinated and unvaccinated groups regarding the reinfection rate. But it may show a piece of evidence that COVID-19 vaccination plays an important clinical role in reducing the severity of COVID-19 infection.