Basic Concepts in Immunity
 Antibodies
 Protein substances or
Globulins derived from
B and T lymphocytes
 Formed by the body as a defensive response
 Titers (concentrations) can be measured to
specific antigens
 Antigen
 Foreign substance or seen by the body as
foreign
 Stimulates antibody production
Host Defense Mechanisms
 Active Immunity (natural and artificial)
 Body produces antibodies in reaction to antigen (e.g.
natural~acquired, and artificial~vaccinations)
 Typically takes 2-3 weeks to confer immunity
 Passive Immunity (natural and artificial)
 “borrowed” in 3 ways:
Injection of serum with antibodies produced by
another host (e.g., immunoglobulin)
Placental transfer (short-term immunity)
Breastfeeding
 Immunity is immediate
Herd Immunity
 Resistance of group or population to spread of
specific disease through group
 Resistance due to high proportion of population
immune to disease (usually due to previous
immunization or infection)
 Theoretically, when 85-90% of population is
immune, herd immunity should protect other 1015%
However localized outbreak could occur if not
well distributed

http://www.health.harvard.edu/video/herd-immunity/
Source: JHSPH Open CourseWare. Fundamentals of Epidemiology
Carrier of Communicable Disease
 Harbors infectious agent
 Asymptomatic
No overt signs or symptoms
 Can be transmitted to others
 Can be carriers during incubation period
or for long periods of time (chronic
carriers)
 “Typhoid Mary”

http://www.youtube.com/watch?v=w0dYpUjr-Cg
Vaccination
 Active immunity produced by vaccine
 Immunity and immunologic memory similar to natural
infection but without risk of disease
Classification of Vaccines
 Live attenuated
 viral
 bacterial
 Inactivated
Inactivated Vaccines
Whole
 viruses
 bacteria
Fractional
 protein-based
 toxoid
 subunit
 polysaccharide-based
 pure
 conjugate
Principles of Vaccination
General Rule
The more similar a vaccine is to
the disease-causing form of the
organism, the better the immune
response to the vaccine
Live Attenuated Vaccines
 Attenuated (weakened) form of the "wild"
virus or bacterium
 Must replicate to be effective
 Immune response similar to natural
infection
 Usually produce immunity with one dose*
*except those administered orally
Live Attenuated Vaccines
 Severe reactions possible
 Interference from circulating antibody
 Fragile – must be stored and handled
carefully
Live Attenuated Vaccines
 Viral
measles, mumps,
rubella, varicella/zoster,
yellow fever, rotavirus,
intranasal influenza,
rotavirus, vaccinia
 Bacterial
BCG, oral typhoid
Inactivated Vaccines
 Cannot replicate
 Generally not as effective as live vaccines
 Less interference from circulating antibody
than live vaccines
 Generally require 3-5 doses
 Immune response mostly humoral
 Antibody titer may diminish with time
Inactivated Vaccines
Whole-cell vaccines
 Viral
polio, hepatitis A,
rabies, influenza*
 Bacterial
pertussis*, typhoid*
cholera*, plague*
*not available in the United States
Inactivated Vaccines
Fractional vaccines
 Subunit
hepatitis B, influenza,
acellular pertussis,
human papillomavirus,
anthrax
 Toxoid
diphtheria, tetanus