Active immunization. In active immunization, the immune system is stimulated by administration of vaccines to develop a disease-specific immunity. Table 1.12 lists the vaccine groups used in active immunization. Table 1.13 shows as an example the vaccination schedule recommended by the Advisory Committee on Immunization Practices of the USA (www.cdc.gov/nip). Recommended adult immunization schedules by age group and by medical conditions are also available in the National Immunization Program Website mentioned above. The vaccination calendars used in other countries deviate from these proposals in some details. For instance, routine varicella and
Table 1.12 Vaccine Groups Used in Active Immunization
Living pathogens with reduced virulence (attenuated)
Purified microbial immunogens
Vaccination protection often not optimum, vaccination has to be repeated several times
Optimum vaccination protection; a single application often suffices, since the microorganisms reproduce in the vaccinated person, providing very good stimulation of the immune system; do not use in immunocompromised persons and during pregnancy (some exceptions)
Often recombinant antigens, i.e., genetically engineered proteins; well-known example: hepatitis B surface (HBs) antigen
Chemically purified capsular polysaccharides of pneu-mococci, meningococci, and Haemophilus influenzae serotype b; problem: these are T cell-independent antigens that do not stimulate antibody production in children younger than two years of age
Coupling of bacterial capsular polysaccharide epitopes to proteins, e.g., to tetanus toxoid, diphtheria toxoid, or proteins of the outer membranes of meningococci; children between the ages of two months and two years can also be vaccinated against polysaccharide epitopes
Bacterial toxins detoxified by formaldehyde treatment that still retain their immunogen function
DNA vaccines. Purified DNA that codes for the viral antigens (proteins) and is integrated in plasmid DNA or nonreplicating viral vector DNA. The vector must have genetic elements—for example a transcriptional promoter and RNA-processing elements—that enable expression of the insert in the cells of various tissues (epidermis, muscle cells)
Anti-idiotype-specific monoclonal antibodies
Vaccinia viruses as carriers of foreign genes that code for immunogens
Table 1.13 Recommended Childhood and Adolescent Immunization Schedule-United States, 2004
1. Hepatitis B vaccine (HepB).
Infants born to HBs-Ag-positive mothers should receive HepB and 0.5 ml HepB Immune Globulin within 12 h of birth at separate sites.
2. Diphtheria (D) and tetanus (T) toxoids and acellular pertussis (aP) vaccine (DTaP). The term "d" refers to a reduced dose of diphtheria toxoid.
3. Haemophilus influenzae type b conjugate vaccine (see Table 1.12).
4. Measles, mumps, and rubella vaccine (MMR). Attenuated virus strains.
5. Varicella vaccine.
Varicella vaccine is recommended for children who lack a reliable history of chickenpox.
The heptavalent conjugate vaccine (PCV) is recommended for all children age 2-23 months. Pneumococcal polysaccharide vaccine (PPV) can be used in elder children.
The "killed virus vaccine" is recommended in selected regions and for certain high-risk groups. Two doses should be administered at least six months apart.
Influenza vaccine is recommended annually for children with certain risk factors (for instance asthma, cardiac disease, sickle cell disease, HIV, diabetes etc.). Children aged < eight years who are receiving influenza vaccine for the first time should receive two doses separated at least four weeks.
pneumococcal vaccinations are not obligatory in Germany, Austria, and Switzerland (see www.rki.de). To simplify the application of vaccines, licensed combination vaccines may be used whenever any components of the combination are indicated and the vaccine's other components are not contrain-dicated. Providers should consult the manufacturers' inserts for detailed information.
Passive immunization. This vaccination method involves administration of antibodies produced in a different host. In most cases, homologous (human) hyperimmune sera (obtained from convalescent patients or patients with multiple vaccinations) are used. The passive immunity obtained by this method is limited to a few weeks (or months at most).
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