A huge effort has been made to produce and deliver vaccinations at an unprecedented level as part of the global fight against the COVID-19 pandemic. the threat of breakthrough infections has persisted, casting doubt on the effectiveness of these shots and the persistent difficulties in controlling the pandemic. Aim of the study to find the prevalence of breakthrough covid19 infection and its associated risk factors. We conducted cross sectional study enrolled 200 healthcare workers from Al-Diwanyiah governorate. The participant was asked to answer a structured questionnaire who were either interviewed face-to-face by the authors or filled by the participant. The study involved 200 patients with Covid-19 vaccinations, with 47% aged 28-37, and 5% elderly. 55% were female, with 25% doctors, 22.5% pharmacists, 6% dentists; there were 77 cases with post-vaccination infections in overall. After immunization, the prevalence of COVID-19 infection was 39%, there is no statistically significant association (p=0.202) between the age category and infection severity. However, there is a statistically significant association (0.012) between severity and gender. Regarding to the worker's place of employment, there was a statistically significant association (p=0.004) between the severity of infection and all cases of severe illness among the pharmacies group. The findings underscore that while breakthrough infections can occur, particularly among healthcare workers, vaccination remains a vital tool in mitigating severe illness and preventing hospitalizations. This reinforces the critical role of continued vaccination efforts in controlling the spread and impact of COVID-19.