| Study characteristics |
| Methods |
Case cross‐over to investigate the association between MMR vaccination and aseptic meningitis in Korean children |
| Participants |
Children aged 13 to 29 months. The design divides the study period (1 year of 365 days) into a hazard period (42 days after MMR, or before meningitis as defined by the authors) and a control period of 323 days. |
| Interventions |
Immunisation with MMR (vaccine type not stated) |
| Outcomes |
Cases of aseptic meningitis before and after immunisation |
| Funding Source |
Government |
| Notes |
There is a likelihood of selection bias, which the authors dismiss as they say that moving (probable cause of wrong phone numbers) is not associated with MMR exposure. The missing 27% of hospital records is also worrying. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| CCO ‐ case selection |
Low risk |
Adequate ‐ record linkage ‐ independent validation |
| CCO ‐ exposure |
Unclear risk |
Self‐reported ‐ study does not distinguish between 2 types of MMR vaccine |
| CCO ‐ risk and control periods |
Low risk |
Adequate ‐ risk and control period are well‐defined |
| CCO ‐ comparability |
Unclear risk |
Not clearly documented |
| Summary Risk of Bias assessment |
Unclear risk |
We had concerns regarding at least 1 domain such that some doubt is raised about the results. |
