That is not a vaccine. No one calls corticosteroids or antibiotics vaccines yet both meet the definition of lowering the probability someone will dies from an infection. So does taking care of yourself, getting exercise, eating a healthy diet, not sitting still all day, and a large swath of other things none of which are called vaccines.
"a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease."
Steriods and antibodies don't meet this definition. No vaccine has a 100% success rate, so reducing symptoms doesn't make it not a vaccine.