EXPRESS: A Sentiment Analysis Study for Reflecting Society Insights on COVID-19 Vaccine Mid-Term Side Effects

Social media discourse has the capacity to influence public perceptions of health-related issues. Understanding how vaccine side effects are discussed online is therefore important for anticipating potential reactions—such as acceptance or hesitancy—toward vaccines that may be deployed in future outbreaks. This study examines public perceptions of the medium-term side effects of COVID-19 vaccines in Turkey by analyzing Turkish-language Twitter posts from the post-pandemic period. Using a hybrid sentiment-analysis approach combining BERT-assisted labeling with machine-learning classification, we evaluated the polarity distribution of tweets related to the BioNTech and Sinovac vaccines. Results indicated that negative sentiment predominated for both vaccines, with 69.85% negative tweets for BioNTech and 44.72% for Sinovac, ensuring a model accuracy of 0.94 and 0.82, respectively. Analysis of frequently occurring terms indicated that the colloquial phrase “heart attack” appeared most often among side-effect-related expressions; however, this pattern reflects only online discourse rather than clinical evidence. Nonetheless, this pattern aligns with medical discussions emphasizing myocarditis as a notable short- and medium-term post-vaccination concern. The findings elucidate the portrayal of vaccine side effects in Turkish social media and have the potential to contribute to the development of evidence-based health communication strategies for forthcoming vaccination campaigns.