What is a vaccine?

• We use the terms "vaccine" and "immunization" interchangeably
• Strictly speaking, there is a difference
• When a person is infected with a germ (measles, for example), the body makes antibodies to fight the germ
• In many cases, those antibodies last forever
• this keeps the person from catching measles again
• It's better to get the person to create the antibodies without making them suffer the disease
• that's what vaccines do
• a tiny bit of antigen is given: enough to cause antibody production, but not enough to cause significant illness

Kinds of Vaccines

• Live attenuated vaccine
• For example, the oral polio vaccine
• This kind of vaccine is capable of causing illness, but does so very rarely and usually in a mild form
• (the recommendation was switched to the injectable polio vaccine a few years ago, to eliminate those rare cases of vaccine-associated polio)
• Killed vaccine
• For example, the injectable polio vaccine
• The virus is dead
• There is no way that it can cause disease
• Toxoid
• For example, the tetanus vaccine
• The vaccine contains a protein, which is just a part of the infectious agent
• There is no way that it can cause disease

Booster doses

• A few vaccines only have to be given once per lifetime
• Most vaccines require one to several "booster" doses
• The schedule varies from vaccine to vaccine; we'll let you know
• The amount of antibody made after the first dose is not always enough to fully protect the recipient
• The next dose causes an amnestic response, producing more antibody

Herd Immunity

• Not only does getting the vaccine protect the person who gets it, it also protects other people
• However, you can’t count on the other people to get vaccinated to protect you

Vaccine Effectiveness

• Most vaccines are between 70% and 90% effective
• No vaccine is 100% protective