• Immunization enhances or initiates resistance to infectious diseases
  • Protection from immunization occurs through several mechanisms:
    • Passive immunization: Administration of purified antibodies or passive transfer of maternal antibodies through the placenta/breast milk
    • Active immunization: Stimulation of immune system, producing IgM antibodies after 7–10 d followed by IgG antibodies, peaking between 2–6 wk
  • Oral and nasal vaccines induce mucosal secretory IgA antibodies while parenteral vaccines may not. Improper administration (route, dose, bad storage, etc.) may result in decreased immunity


  • Several types of vaccines are available:
    • Live attenuated (weakened) viruses (e.g., varicella [VZV]; measles, mumps, rubella [MMR]; rotavirus) replicate in the host and induce an immune response:
      • May cause serious infections in the immunocompromised
    • Inactivated (or killed) vaccines (e.g., polio [IPV], hepatitis A [HepA], some influenza, pertussis) are safe in patients with compromised immune system
    • Toxoid, subunit, or conjugate vaccines (e.g., diphtheria, tetanus, Haemophilus influenzae b [Hib], human papilloma virus [HPV], Pneumococcus, Meningococcus) use antigenic portions of toxins, proteins, or carbohydrates from viruses or bacteria to induce immune response
    • Hepatitis B (HepB) vaccine uses recombinant DNA technology
  • Several combination vaccines are also available but have an increased cost:
    • Comvax (HepB and Hib)
    • Pediarix (diphtheria and tetanus toxoids and acellular pertussis adsorbed [DTaP], HepB, and IPV combined)
    • Pentacel (DTaP, IPV, and Hib)
    • Twinrix (HepA and HepB)
    • MMRV (MMR and VZV)


  • The incidence of several life-threatening illnesses has been markedly reduced with widespread immunization use:
    • Polio caused by wild-type viruses has been eliminated from the Western Hemisphere
    • Hib, diphtheria, and tetanus vaccines have nearly eliminated these invasive diseases among children in North America
    • The incidence of measles, rubella, and VZV has also declined; sporadic in unimmunized communities and foreign travelers to the U.S.
    • 7-valent conjugate pneumococcal vaccine (introduced in 2000) and its 13-valent replacement (2010) have reduced invasive disease for vaccine serotypes (meningitis, pneumonia, bacteremia) >90%
    • Rotavirus infections have declined 58–90% in the U.S. since the introduction of routine vaccination in infants
    • Global surveillance of influenza activity allows for annual production of vaccines against seasonal influenza. Inactivated vaccines are available for IM administration and live attenuated virus vaccines can be given via the nasal route
  • Immunization recommendations and schedules are based on epidemiology, individual risks for disease and exposure, as well as vaccine safety and efficacy:
    • Infants and young children are vaccinated against common childhood diseases, but some vaccines are not immunogenic (e.g., pneumococcal capsular polysaccharide antigen vaccine) or may be dangerous (e.g., MMR, VZV) in infants
    • Pregnant women are recommended to receive Tdap and inactivated influenza, but should not receive other live virus vaccines
    • Specific recommendations exist for other at-risk groups including international travelers, the elderly, health care workers, and immunocompromised individuals
    • Respiratory syncytial virus is available for high risk patients

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