A Piggyback vaccine is a vaccine that takes part of a harmful viral protein, and puts it into the DNA of a harmless virus.
Piggyback vaccines are called this because the virus sort of rides in on the other. Traditionally, vaccines were made by killing the disease agent. Now a modified virus displays piggybacked surface proteins, to which immune system makes antibodies.
When the vaccine is injected, the antibody production prevents future infection from each virus in the vaccine.
Below is the steps in constructing a subunit, or piggyback, vaccine for the herpes simplex virus.
via kwout
Federal law requires that healthcare staff provide a VIS to a patient, parent, or legal representative before each dose of certain vaccines.
See Vaccine Information Statements (VISs) produced by the CDC that explain both the benefits and risks of a vaccine to vaccine recipients.