Sadly the fallacy of the "argument from ignorance", does not work even in the twenty first century and on the web, the world may be moving in that direction, but we are not there yet. And if you do not know about the definition of the "argument from ignorance" look it up.

[nature.com]
Your question makes no sense since vaccines do prevent disease but this does explain the difference between therapies.

If a vaccine works, it is therapeutic?

Pfizer-BioNTech and Moderna
DNA and RNA vaccines use fragments of genetic material made in the lab. These fragments code for a part of the virus (such as its spike protein). After the vaccine is injected, your body uses instructions in the DNA/RNA to make copies of this virus part (or antigen). Your body recognises these and mounts an immune response, ready to protect you the next time you encounter the virus. mRNA vaccines do not use the live virus that causes COVID-19. They do not affect or interact with our DNA in any way. mRNA never enters the nucleus of the cell, which is where our DNA (genetic material) is kept. The cell breaks down and gets rid of the mRNA soon after it is finished using the instructions. Pfizer-BioNTech and Moderna are (messenger) mRNA vaccines.

Oxford/AstraZeneca
Virus vector vaccines use a virus, often weakened and incapable of causing disease itself, to deliver a virus antigen into the body. It is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees. It has been modified to contain genetic material shared by the coronavirus - although it can't cause the illness. The virus’ ability to infect cells, express a large amount of antigens and in turn trigger a strong immune response is how the virus vector is effective. One high-profile example is the University of Oxford/AstraZeneca vaccine.
[theconversation.com]
[cdc.gov]

Let's look at specific definitions:

Monoclonal antibody therapy is a form of immunotherapy that uses monoclonal antibodies to bind monospecifically to certain cells or proteins. The objective is that this treatment will stimulate the patient's immune system to attack those cells.

Vaccine - 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.
"every year the flu vaccine is modified to deal with new strains of the virus"