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.