It's clear from the passage that vaccines ....... .

Immunity is the ability of a person to resist or
overcome a disease. The blood contains certain
substances called antibodies that make immunity
possible. The body produces these antibodies,
which light and destroy the bacteria and viruses that
cause disease. Each type of antibody is effective
against only one particular disease. No person has
immunity or resistance to all diseases. Immunity can
be either natural or acquired. Natural immunity is
that which a person is born with and can vary even
within a community. Acquired immunity is that which
results from a person having had a disease or
having been vaccinated by being injected with dead
or weak viruses or bacteria. In recent times, many
diseases have been eliminated through this type of
immunity.