Immunizations

Basics

Description

  • 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

Etiology

  • Several types of vaccines are available:
    • Live attenuated (weakened) viruses (eg, 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 (eg, polio [IPV], hepatitis A [HepA], some influenza, pertussis) are safe in patients with compromised immune system
    • Toxoid, subunit, or conjugate vaccines (eg, 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
    • Most COVID-19 vaccines use mRNA, which teaches cells to make a protein to trigger an immune response, others contain protein subunits with adjuvants to trigger immune response:
      • mRNA vaccines can be created much more quickly than traditional vaccines

Epidemiology

  • 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
    • Incidence of measles, rubella, and VZV has also declined; sporadic in unimmunized communities and foreign travelers
    • 7- and 13-valent conjugate pneumococcal vaccines have reduced invasive disease for vaccine serotypes (meningitis, pneumonia, bacteremia) >90%
    • Rotavirus infections declined 58–90% in the US since the introduction of routine vaccination in infants
    • The COVID vaccine prevented an estimated 18.5 million hospitalizations and 3.2 million deaths in the first 2 yr of availability
  • 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 (eg, pneumococcal capsular polysaccharide antigen vaccine) or may be dangerous (eg, 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 (RSV) is available for infants, pregnant women, and those >60 y/o with risk factors

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