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 10-15%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

viruses bacteria

protein-based toxoid subunit

polysaccharide-based pure conjugate

Whole

Fractional

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

Viral polio, hepatitis A, rabies, influenza*

Bacterial pertussis*, typhoid*cholera*, plague*

Whole-cell vaccines

*not available in the United States

Inactivated Vaccines

Subunit hepatitis B, influenza,acellular pertussis,

human papillomavirus, anthrax

Toxoid diphtheria, tetanus

Fractional vaccines