The Basics of Pediatric Immunizations

Elizabeth Farren, PhD, RN; Melanie McEwen, PhD, RN

Disclosures

NAINR. 2004;4(1) 

In This Article

Overview of Communicable Disease, Immunity, and Immunizations

In the 1880's and 1890's, Robert Koch established that a different microbe causes each infectious disease. Koch defined a process by which a specific causative organism could be identified by demonstrating that: 1) the suspected organism is present in every case of the disease; 2) the organism can be isolated and grown in the laboratory; 3) an animal will develop the disease when injected with the laboratory-grown culture; and 4) the organism can be isolated from the newly infected animal and the process repeated.[2]

Since Koch's time, scientists have recognized that communicable diseases do not occur in a vacuum, but are the result of the exposure of a susceptible individual (one who has not had the disease or who has not been immunized) to a disease-causing organism. This can be through direct person-to-person transmission by coughing, sneezing, kissing, or sex; through indirect transmission, which involves spread of the organism via inanimate objects such as contaminated food, water, money, or soiled tissues; or by animals (eg, rabies) or insects (eg, malaria). The communicability of an infectious agent causes the threat of ongoing disease, not just in an individual but also in whole populations.

Researchers and epidemiologists have determined that a chain of infection must exist for a disease to be communicable. The chain of infection requires several links including 1) a pathogen of causation; 2) a reservoir, or place where the pathogen lives; 3) a method of transmission; and 4) a susceptible host.[2] Many public health advances through the years have successfully fought disease by countering the first three links of the chain of infection. Eliminating the causative organisms responsible for disease defeats the first link. This is frequently possible and is commonly accomplished by such means as cleaning, sterilizing, and using disinfectants. The second link can be targeted by the elimination or minimization of reservoirs or hosts that allow the organism to grow. An example of this is killing mosquitoes or removing their breeding areas to prevent malaria. Prevention of transmission, the third link, is accomplished in a variety of ways. Examples include use of surgical masks and gloves, quarantine of infected individuals, and control of vectors (eg, rats that carry plague). Immunization addresses the fourth link-host susceptibility.

Immunity to a communicable disease protects an individual from infection. There are several types of immunity. Innate immunity occurs if the individual is born resistant to a specific organism. Acquired immunity may be active or passive. Active immunity comes from actual exposure to an organism (natural immunity) or through obtaining the appropriate vaccine (artificially induced immunity). Active immunity requires a competent immune response to the antigen exposure and offers long-term immune protection. Passive immunity is a temporary immunity achieved through transmission of maternal antibodies to a fetus from its mother or by administration of immunoglobulins or antitoxins to a susceptible client.[3]

Immunization is the process of inducing an active immunity or providing immunity passively by administering an immunobiologic agent. Immunobiologic is a term that encompasses three categories of agents: vaccines, toxoids, and immune sera. Vaccines and toxoids are distinctly different agents and yet both induce active immunity. That is, the agents induce the body to respond to their presence with a natural immunologic response to an antigen. Herd immunity denotes an additional form of protection achieved through the active immunization of a significant proportion of the at risk population. By increasing the number of individuals who cannot contract and consequently cannot transmit a disease, a measure of protection is achieved for nonimmunized persons by default.

Vaccines are made from an infecting organism. Viral vaccines can be made from either killed viruses or live attenuated viruses, meaning that the organisms are altered in a way that enables them to multiply in the host but leaves them unable to cause disease. Live attenuated vaccines induce a response in the host more similar to natural infection, and thus may confer lifelong immunity, as would a primary natural infection. This is not always the case, however. For example, measles vaccine, a live attenuated virus vaccine, requires a booster dose. Other live attenuated viral vaccines are Sabin polio (oral) vaccine, and mumps and rubella vaccines.

Killed virus vaccines may be whole viruses, split particles of a virus, or specific fragments (subunits) of a virus. Hepatitis B vaccine is an example of a viral subunit vaccine.[4] Vaccines made from killed organisms always require additional doses at some time after the initial dose and may require additional boosting periodically.

Bacterial vaccines are usually made from whole killed bacteria or specific bacterial wall antigens. Examples of killed or inactivated bacterial vaccines are pertussis, plague, and anthrax. As with the killed viral vaccines, these vaccines do not confer lifelong immunity and must be boosted periodically to preserve effectiveness.

Toxoids are inactivated bacterial toxins. The toxin is modified in vaccine production and is often combined with agents that prolong its absorption and, thus, enhance its antigenicity. The toxoid retains the ability to stimulate antitoxin formation in the recipient and thereby confers active immunity.[4] Toxoids, like the killed biologic vaccines, do not induce lifelong immunity and must be boosted periodically. Tetanus and diphtheria vaccines are examples of toxoids.

Immune sera are sterile solutions containing preformed antibodies derived from human (immune globulin) or equine (antitoxin) sources. Immune sera confer temporary passive immunity, that is, immunity that persists only for the lifetime of the antibodies given in the sera. In general, passive immunity lasts for 6 to 12 weeks.[5] Examples of these sera include immune globulin (Ig), for use against a wide variety of diseases, and Hepatitis B Immune Globulin (HBIG), for therapy after known or suspected exposure specifically to hepatitis B.

Immune globulin is derived from the blood plasma of large donor pools (at least 1,000 per lot of sera) of populations known to have experienced specific diseases. The sera contain primary IgG and trace amounts of IgA and IgM and are treated to remove any infecting agents. Antitoxins are derived from horses that have been immunized with an antigen and allowed to form antibodies. The antibodies (antitoxins) are harvested and used to treat already infected subjects. Monoclonal antibody is sera prepared from a single lymphocyte clone that contains only antibody against a single microorganism. The monoclonal antibody has the lowest potential for allergic response because it is the least complex sera. Immune sera are given when persons are immune deficient, have suffered exposure to a serious disease for which they have no protection, or are experiencing a disease for which an antibody may help avoid injury or complication.

In addition to the active components in immunobiologics, other active and inert ingredients may be present. These include suspending agents, preservatives, stabilizers, antibiotics, and aluminum salts. Vaccine recipients may experience an allergic response to any of these tangential components, as well as to the immunobiologic itself.[4] The use of human immune sera or monoclonal antibody is always preferred if available, because the risk of allergic response is far less, though still considerable, compared with the equine sera.

Immunization of persons/populations is recommended when risk of infection exceeds risk from exposure to immunization material. Consideration should be given to 1) seriousness of the disease and its consequences, 2) likelihood of exposure to the causative organism, and 3) possible hazardous responses to a vaccine. In the case of active immunization, it is also important to assess the recipient's ability to respond to the antigenic challenge of the vaccine by forming appropriate humoral and/or cellular immunity.

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