Well I guess that depends on what you mean by “true immunity”. If you mean not a single cellular infection, then that is ridiculous since true immunity doesn’t exists.
If instead you mean that you develop no symptoms, and cannot pass on the virus, then they indeed can and do (which is why r naught drops).
Now obviously if your “high viral load” is being literally bathed in viruses... then ok. But for many situations, typical viral load and even high viral load situations as seen in health care settings, many vaccines would qualify as giving large percentages of people “true immunity” in the sense of no symptoms and no viral shedding.
Another thing vaccines can do is prevent illnesses caused by toxins. In those cases antigens of toxic compounds generate antibodies to incapacitate a toxoids effect on the body, for example the tetanus and diphtheria vaccines or vaccines against rattlesnake venom.
If instead you mean that you develop no symptoms, and cannot pass on the virus, then they indeed can and do (which is why r naught drops).
Now obviously if your “high viral load” is being literally bathed in viruses... then ok. But for many situations, typical viral load and even high viral load situations as seen in health care settings, many vaccines would qualify as giving large percentages of people “true immunity” in the sense of no symptoms and no viral shedding.
Another thing vaccines can do is prevent illnesses caused by toxins. In those cases antigens of toxic compounds generate antibodies to incapacitate a toxoids effect on the body, for example the tetanus and diphtheria vaccines or vaccines against rattlesnake venom.