One issue with supplements is people tend to think that if one is good, then two might be better, and Vitamin A is actually a bit dangerous, especially if you started hyperdosing kids.
More than one month into a major measles outbreak in western Texas that has sickened 146 people and killed one school-age child, the Centers for Disease Control and Prevention released its first public statement and it highlighted a therapy that has raised some eyebrows among infectious disease experts.
“Measles does not have a specific antiviral treatment,” read the statement, which was posted only on X on Thursday night. “Supportive care, including vitamin A administration under the direction of a physician, may be appropriate.”
tl;dr There is evidence Vitamin A helps with measles in area where people tend to have a deficiency, but it certainly doesn't prevent or cure measles.