en Medicine پژوهشي Research <div style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Times New Roman;"><b>Background:</b> While vaccines provide substantial protection against COVID-19, breakthrough infections remain a concern. This study aimed to determine the Incidence rate of post-vaccination COVID-19 infections among healthcare workers at teaching hospitals in Gorgan, Northeast Iran between 2020 and 2021.<br> <b>Methods:</b> In this cross-sectional study, we enrolled all 527 healthcare workers who had received at least one dose of non-mRNA COVID-19 vaccines. Vaccination data were systematically recorded and analyzed. COVID-19 infection was laboratory-confirmed by RT-PCR testing.<br> <b>Results:</b> The mean age of participants was 35.3&plusmn;9.8 years. Breakthrough infections occurred in 255 participants (48.4%) after primary vaccination (First and second doses) and in 36 cases (6.83%) following booster doses. Incidence rates were significantly higher among internal medicine and infectious disease staff (p=0.006). Temporal analysis revealed peak infection incidence within 4 months post-primary vaccination, with the lowest rates observed >4 months post-booster administration.<br> <b>Conclusion</b>: While breakthrough infections occurred in a substantial proportion of participants after primary vaccination, booster doses were associated with significantly lower infection rates. Further research is needed to assess the impact of vaccination status on disease severity.</span></span></div> COVID-19, Vaccination, Breakthrough infection, Healthcare workers, Non-mRNA vaccines, Iran 0 0 http://jcbr.goums.ac.ir/browse.php?a_code=A-10-55-8&slc_lang=en&sid=1 Samira Eshginia Eshginia@yahoo.com 10031947532846006642 10031947532846006642 No Metabolic Disorders Research Center, Biomedical Research Institute, Golestan University of Medical Sciences, Gorgan, Iran Roghieh Golsha Golsha@yahoo.com 10031947532846006643 10031947532846006643 No Infectious Diseases Research Center, Jorjani Clinical Sciences Research Institute, Golestan University of Medical Sciences, Gorgan, Iran; Department of Infectious Diseases, 5th Azar Hospital, Golestan University of Medical Sciences, Gorgan, Iran; Department of Infectious Diseases, Sayyad Shirazi Hospital, Golestan University of Medical Sciences, Gorgan, Iran Rahmatollah Sharififar Sharififar@yahoo.com 10031947532846006644 0009-0008-7118-4026 No Department of Infectious Diseases, 5th Azar Hospital, Golestan University of Medical Sciences, Gorgan, Iran; Department of Infectious Diseases, Sayyad Shirazi Hospital, Golestan University of Medical Sciences, Gorgan, Iran Negar Broumand Broumand@yahoo.com 10031947532846006645 10031947532846006645 No Department of Surgery, 5th Azar Hospital, Golestan University of Medical Sciences, Gorgan, Iran Fatemeh Mehravar Mehravar10261@yahoo.com 10031947532846006646 10031947532846006646 Yes Ischemic Disorders Research Center, Jorjani Clinical Sciences Research Institute, Golestan University of Medical Sciences, Gorgan, Iran