Cohort Event Monitoring on Adverse Reactions to COVID-19 Vaccines in Seven European Countries: Pooled Results on First Dose: An International Journal of Medical Toxicology and Drug Experience

ABSTRACT

Introduction: COVID-19 vaccines were rapidly authorized leaving many questions and the need to monitor safety intensively. Objective: Multi-national collaboration was established with the aim to monitor the safety of the COVID-19 vaccines through prospective cohort event monitoring in Europe. Methods: A prospective cohort event monitoring study was con- ducted with primary consented data collection in seven countries between December 2020 and November 2021. Participants in Bel- gium, France, Italy, the Netherlands and United Kingdom registered using the LIM web app and received follow-up questionnaires for six months. Participants from Croatia and Germany registered with the OPeN and SafeVac2.0 apps respectively. Rates of self-reported reactions were described by type (solicited, non-solicited), adverse event of special interest (AESI), seriousness, and stratified by vaccine brand. The rate of self-reported adverse reaction was calculated after dose 1 and prior to dose 2 among all subjects who responded with at least one questionnaire. Results: 117,791 participants were included and responded to the first questionnaires after baseline 88,196 from Germany, 27,588 from the Netherlands, 984 from France, 570 from Italy, 326 from Croatia, 89 from the United Kingdom and 38 from Belgium. 89,377 respondents received AstraZeneca, 14,658 BioNTech/Pfizer, 11,266 Moderna and 2490 Janssen. Reporting included all vaccine brands from all coun- tries, except Germany which only included data on Moderna until May 2021 and AstraZeneca until September 2021. Median time to completion was 8 days for the first questionnaire after dose 1 (Netherlands, Belgium, Italy, France, United Kingdom) and 3 days in Croatia. Median age category was 40-49 for all vaccine exposed groups except for BioNtech/Pfizer where median age was 70-79. Fatigue and headache were the most commonly reported solicited systemic adverse reactions, injection site reactions the most common solicited local reaction. AESIs were very rare (< 0.1%) and serious adverse reactions were uncommon (< 1%) across all vaccine brands. Conclusion: This study that collated self-reported data from more than 100,000 COVID-19 vaccine recipients, demonstrated feasibility of setting up and conducting cohort event monitoring across multiple European countries to collect safety data on novel vaccines that are rolled out at scale in populations which may not have been included in pivotal trials. Different vaccination schedules in countries and dif- ferent web applications resulted in some heterogeneity. The study confirmed the safety information in the product labels reactogenic reactions, related to immunogenic response, and local injection site reactions were very common across all vaccines, whereas serious reactions or AESIs were (very) rare.