 Adverse effects of the transtympanic injection will be documented according to the Common Terminology Criteria for Adverse Events v4.0 CTCAE. In addition, to identify unexpected adverse effects of the trial intervention on hearing, a shorter unblinded audiogram will be conducted before proceeding to the second and third transtympanic injections. Data from these audiograms will not be used in the main analysis.The follow-up for audiologic safety monitoring will be continued for one year after the end of the trial. 