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
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