Immunity to a disease is achieved through the presence of antibodies to that disease in a person’s system. Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms. Antibodies are disease-specific. For example, measles antibody will protect a person who is exposed to measles disease, but will have no effect if he or she is exposed to mumps.
There are two types of immunity: active and passive.
Active immunity results when exposure to a disease organism triggers the immune system to produce antibodies to that disease. Exposure to the disease organism can occur through infection with the actual disease (resulting in natural immunity), or introduction of a killed or weakened form of the disease organism through vaccination (vaccine-induced immunity). Either way, if an immune person comes into contact with that disease in the future, their immune system will recognize it and immediately produce the antibodies needed to fight it.
Active immunity is long-lasting, and sometimes life-long.
Passive immunity is provided when a person is given antibodies to a disease rather than producing them through his or her own immune system.
A newborn baby acquires passive immunity from its mother through the placenta. A person can also get passive immunity through antibody-containing blood products such as immune globulin, which may be given when immediate protection from a specific disease is needed. This is the major advantage to passive immunity; protection is immediate, whereas active immunity takes time (usually several weeks) to develop.
However, passive immunity lasts only for a few weeks or months. Only active immunity is long-lasting.
Journal Articles on This Topic
- Fox JP, Elveback L, Scott W, et al. Herd immunity: basic concept and relevance to public health immunization practices. Am J Epidemiol 1971; 94:179–89.
- Anderson RM, May RM. Vaccination and herd immunity to infectious diseases. Nature 1985; 318:323–9.
- Fine PEM. Herd immunity: history, theory, practice. Epidemiol Rev 1993; 15:265–302.
- Fine PEM, Mulholland K. Community immunity. In: Plotkin SA, Orenstein WA, Offit PA eds. Vaccines. 5th ed. Chapter 71. Philadelphia, PA: Elsevier Inc., 2008:1573–92.
- John TJ, Samuel R. Herd immunity and herd effect: new insights and definitions. Eur J Epidemiol 2000; 16:601–6.
- Stephens DS. Vaccines for the unvaccinated: protecting the herd. J Inf Dis 2008; 197:643–45.
- Heymann D, Aylward B. Mass vaccination in public health. In: Heymann D, ed. Control of communicable diseases manual. 19th ed. Washington, DC: American Public Health Association, 2008.
- Topley WWC, Wilson GS. The spread of bacterial infection: the problem of herd immunity. J Hyg 1923; 21:243–9.