We appreciate the insightful comments from Dr. Hsu and colleagues on our study. We provide responses to the raised concerns.
Our study used the self-controlled case series (SCCS) method, which is recognized as a standard design in postlicensure vaccine safety research. , The SCCS method is particularly suitable for assessing transient exposures such as vaccination and inherently controls for time-invariant confounders, including age, sex, and comorbidities by comparing time periods within the same individual. , Given this design characteristic, additional adjustment such as propensity score matching is generally not needed or applied in the SCCS design. We intentionally avoided a traditional cohort design because individuals who receive vaccination may differ systematically from those who do not, in terms of both underlying health status and healthcare use behavior. In claims data, these differences are often unmeasurable and cannot be fully adjusted for, even with large sample sizes.
Contrary to the concern about potential misclassification of COVID-19 infection, our study defined COVID-19 infection based on polymerase chain reaction–confirmed cases, recorded in the Korea Disease Control and Prevention Agency database. Since the beginning of the pandemic, Korea implemented a nationwide polymerase chain reaction testing infrastructure, including drive-through and community screening centers. All confirmed cases were mandatorily reported and recorded in a database maintained by the Korea Disease Control and Prevention Agency, ensuring high data accuracy. We acknowledge, however, that some infections may have gone unreported, particularly when individuals avoided testing to avoid quarantine restrictions or to reduce work-related disruptions.
Discrepant findings across studies on vaccine-associated ocular events can occur and likely reflect differences in study design, population selection, exposure and outcome definitions, and confounding control strategies. , The understanding of vaccine safety requires consideration of the cumulative evidence from various studies.
CRediT authorship contribution statement
SUNGSOON HWANG: Investigation, Writing – original draft. SE WOONG KANG: Investigation, Writing – review & editing.
Declaration of interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
See the original article for any disclosures of the authors.
References
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