eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2022-06-30 15 2 993 1003 10.13005/bpj/2435 44359 article Efraín Navarro-Olivos 1 Francisco J. Magos-Vázquez 2 María del Rosario Sánchez-Navarro 3 Daniel A. Díaz-Martínez 2 lia Lara-Lona 4 María de Jesús Gallardo-Luna 5 Directorate of Teaching and Research, Institute of Public Health from Guanajuato State, Guanajuato, México Directorate of Health Services, Institute of Public Health from Guanajuato State, Guanajuato, México State Laboratory of Public Health, Institute of Public Health from Guanajuato State, Leon, México Department of Medicine and Nutrition, Division of Health Sciences, Campus Leon, University of Guanajuato, León, Mexico Department of Research and Technological Development, Directorate of Teaching and Research, Institute of Public Health from Guanajuato State, Guanajuato, Mexico The Severe Acute Respiratory Syndrome Coronavirus 2, first detected in Wuhan, China, in 2019, had spread all over the world. It has caused the COVID-19 pandemic. Nowadays, there are effective and safe vaccines proven against this virus. The goal of this study was to verify it among health-care workers from the Institute of Public Health from Guanajuato State who received the BioNTech/Pfizer vaccine. For this purpose, we designed a quantitative cross-sectional study. The database was obtained from a previous strategy program by the Institute of Public Health from Guanajuato State called ENSERO-COVID. The available data consisted of two chemiluminescence measures of the IgG anti-Spike antibodies after one and six months of the BioNTech/Pfizer vaccine two doses application. The survey also included self-reported reactions to this vaccine. Frequency tables are presented for descriptive purposes. We performed the chi-square test, the z test for proportions, and the t-test for comparisons. Also, two linear regression models were fitted between the first and second chemiluminescence levels stratifying by prior infection by SARS-CoV-2. The database consisted of 177 records. Of them, 45 (25.4%) were positive for SARS-CoV-2 before vaccination. Only one person did not react to the two doses of vaccine application. Most of the self-reported reactions ceased in a short period -less than three days-. The differences observed, regarding chemiluminescence levels, between those with and without prior infection by SARS-CoV-2 were not statistically significant. More analyses are required to assess the long-term effects of the BioNTech/Pfizer ® vaccine. https://biomedpharmajournal.org/vol15no2/reactivity-and-safety-of-biontechpfizer-vaccine-anti-sars-cov-2-in-health-personnel-from-the-mexican-state-of-guanajuato/ BioNTech/Pfizer vaccine  COVID-19  Health-Care professional vaccination  IgG antibodies  SARS-CoV-2