Introduction: COVID 19 Vaccination which was started in January 2021 in India and is one of the major hopes for ending the pandemic. This study was done in a tertiary care hospital in India to understand the adverse events following COVID 19 immunization. Methodology: This was a longitudinal study done in a tertiary care hospital in Thiruvallur district. By universal sampling, 1200 healthcare workers who got vaccinated in the hospital from January 20 to January 30, 2021 were study participants. Pre-tested semi structured questionnaire was used for data collection which was used for collecting data regarding socio-demographic details, adverse events immediately following vaccination and late adverse events which were followed up after 48 hours by telemonitoring. Results: Around 3.7% of the study participants had immediate reactions, 6.3% developed reactions in waiting room and 50.4% developed late reactions which were mild to moderate in severity and got relieved on medication and rest. Female sex, previous COVID infection and age less than 30 years had statistically significant association with late vaccine reactions Conclusion: The study shows that COVID vaccine adverse events though present were mild to moderate in severity and they should not be the reason to defer or refuse COVID vaccination.