His fast is not invalidated, which is the correct view, as long as he did not intentionally vomit; because there was no act of breaking the fast, which is swallowing, and its meaning is the same; since he does not get nourished by it. However, if he did it intentionally and it filled his mouth, his fast is invalidated as soon as it comes out, even if he does not swallow the vomit again. Refer to Al-Tahbiin 1: 325-326, and Al-Radd Al-Muhtar 2: 111.