4.1 Study limitations
There are some limitations to this study. Firstly, due to the unique nature of vaccine research, all studies included had no control group. Although it was a single-arm meta-analysis, the extremely low pooled incidence rate can still reflect the safety of the vaccine. Secondly, the overall heterogeneity in the analysis of the results of this study was large, and despite the use of a random-effects model, there may still exist the presence of uncontrollable confounding factors. We tried to conduct multiple subgroup analyses stratified by confounding factors such as age, sex, comorbidities, etc to test the stability of the results, but these factors could not be further corrected due to the lack of raw data; and we also performed bias analysis and sensitivity analysis to examine the influence of a specific study on the overall results, confirming that our included studies were large and of high quality and that individual studies had little effect on the overall results, so we judged the results to remain reliable. Thirdly, due to the significant variation in the number of publications for different diseases, we ultimately included only three types of diseases (MS, MG, NMOSD) after the screening, mainly because these diseases are rare and thus have fewer relevant studies. Finally, most of the studies were conducted in 2022, during which the Omicron variant was dominant, and the incidence of adverse events may differ across different strains of the virus.