To clarify: are you saying that it is not possible to do [any] vaccine research in general without this specific type of gain-of-function research? Citations? Looking to educate myself.
Quoting Dr. Anthony Fauci, former director of the National Institute of Allergy and Infectious Diseases:
"Some want to pass a law: All gain-of-function should be stopped. But if all gain-of-function stops, you will have no vaccines for flu. You will have no vaccines for any of the other diseases, because all of that manipulates a virus or a pathogen to gain a certain function to be able to make a vaccine."