Words have definitions.
Retard – delay or hold back in terms of progress, development, or accomplishment.
“our progress was retarded by unforeseen difficulties”
A study showing that the shot may have doubled *cognitive impairment* warrents the use or “retard” in its it proper use case. Just because the word invokes some bad feeling doewnt mean it use should be forbidden. Whenever i want to talk about retarding a engine the comment gets flagged even though thats rthe proper term to use in that case as well.