A host body uses its “immune system” to fight off a virus. Once any foreign substance is introduced, the body responds through what is called an “immune response”—the way the body produces antibodies. These antibodies are specific to each invader and can be thought of as natural “antibiotics”—destroying an invader and preventing the host from contracting the same disease in the future.

The antibodies specific to the infection take about seven days to work. In the meantime, the body’s cells that are exposed and infected with the virus produce naturally occurring interferons, or proteins (called cytokines, proteins that carry signals between cells). They stop a disease when they are released into the bloodstream and then bind to receptors on the surface of cells. They are usually released within three to five days after exposure to the virus, preventing infection in neighboring cells until the antibodies are made. (Note: in contrast to antibodies, interferons are not virus specific, but host specific; for example, viral infections of human cells are inhibited only by human interferons.)