Please find below separate guidance on complex clinical trials and clinical trials involving seasonal vaccines.
Complex clinical trials may require special handling during the initial application process and when submitting subsequent modifications in CTIS. Guidance on how to submit complex clinical trials and manage matters such as EU CT numbers, amendments to the master protocol, safety information, and notifications can be found in the homepage Guidance for Non-Commercial Clinical Trials and SMEs under the section “Complex Clinical Trials.”
In clinical trials involving seasonal vaccines, the vaccine strains to be used in the trial may not be known at the time of application or may be updated subsequently. Please refer to the Guidance for Non-Commercial Clinical Trials and SMEs under the section “Seasonal Vaccine Trials” for information on how to submit such trials and manage related changes in CTIS.
Excerpt from the official page. The original is authoritative.