BACKGROUND: The safety profile of COVID-19 vaccines in immunocompromised patients has not been comprehensively evaluated. AIM: To measure the frequency of patient-reported adverse drug reactions (ADRs) related to the first/second/booster dose of COVID-19 vaccine in immunocompromised subject versus matched cohort. As a secondary objective, the time course, evaluated as time to onset (TTO) and time to recovery (TTR), of COVID-19 vaccine-related ADRs was explored. METHODS: A prospective cohort study, based on electronic questionnaires filled by vaccinees from 11 European countries in the period February 2021 to February 2023 was conducted. All immunocompromised vaccinees who provided informed consent and registered to the project’s web-app within 48 h after first/booster vaccine dose administration of any EMA-authorised COVID-19 vaccine were recruited. Participants filled baseline and up to six follow-up questionnaires (FU-Qs) over 6 months from vaccination, collecting information on suspected COVID-19 vaccine-related ADRs. As a control group, non-immunocompromised vaccinees from the same source population were 1:4 matched by sex, age, vaccine dose, and brand. A descriptive analysis of demographic/clinical characteristics of vaccinees was conducted. Heatmaps of the frequency of solicited ADRs, stratified by gender and vaccine brand, were generated. Median TTO/TTR of reported ADRs were visualised using violin/box-plots. RESULTS: A total of 773 immunocompromised vaccines were included in the analyses. Most participants were females (F/M ratio: 2.1 and 1.6) with a median age of 56 (43-74) and 51 (41-60) years, at the first vaccination cycle and booster dose, respectively. Injection-site pain and fatigue were the most frequently reported ADRs in immunocompromised vaccinees with higher frequency than matched control, especially after the first dose (41.2% vs 37.8% and 38.2% vs 32.9%, respectively). For both cohorts, all solicited ADRs were more frequently reported in females than males, and in those who had received a first dose of the Vaxzevria vaccine. Dizziness was the most frequently reported unsolicited ADR after the first dose in both groups (immunocompromised subjects: 2.5% and matched controls: 2.1%). At the booster dose, lymphadenopathy (3.9%) and lymphadenitis (1.8%) were the most reported unsolicited ADRs for immunocompromised subjects and matched controls, respectively. A very low number of subjects reported adverse event of special interest (AESI) (2 immunocompromised, 3 matched controls) and serious ADRs (5 immunocompromised, 5 matched controls). A statistically significant difference among study cohorts was observed for median TTO after the booster dose, and for median TTR after the first vaccination cycle and booster dose (p < 0.001). CONCLUSION: The overall safety profile of COVID-19 vaccines in immunocompromised people was favourable, with minor differences as compared to non-immunocompromised vaccinees. Participants mostly experienced mild ADRs, mainly reported after the first dose of Vaxzevria and Jcovden vaccines. Serious ADRs and AESI were rare.