It's caused by the immune system making antibodies to the killed viruses in the vaccine that help a person fight off the flu.

CNN: Flu shot myths addressed

Jamie Murphy in What Every Parent Should Know About Childhood Immunization and Eleanor McBean in The Poisoned Needle recount many case histories of children and adults maimed and killed by the smallpox vaccine, including many gruesome old photographs.

FORBES: When Americans Rejected Small Pox Vaccines

Salk's vaccine, developed in the 1950s, involved injecting a virus that was "killed, " while Sabin's vaccine -- which he worked on in the 1960s and which was administered orally -- contained a weakened version of polio.

CNN: Why polio hasn't gone away yet

The viruses in flu shots are killed during the production of the vaccine, which means they cannot cause infection.

CNN: Flu shot myths addressed

All the component parts of the vaccine are inactivated, killed, so they can't cause the diseases they are protecting against.

BBC: Whooping cough vaccine a 'no-brainer' during pregnancy

The flu vaccine is comprised of killed or inactivated virus (three most likely strains of flu virus based on predictions from the previous flu season).

FORBES: 2013 Flu Season: How to Protect Yourself

In the end, the influenza claimed one life, but the vaccine that was supposed to guard against it killed 32 people and seriously injured hundreds.

ECONOMIST: Vaccines against bioterrorism

According to Forbes contributor Steven Salzberg, a whooping cough epidemic in California that has killed nine babies may be the result of the burgeoning anti-vaccine movement.

FORBES: Too Much Breast Cancer Awareness?