Principles of Immunization¶
Chapter 128 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Vaccines are critical public health interventions, averting over 37 million deaths globally between 2000-2019.
- Vaccines stimulate active immunity through antigen-specific immune responses, with adjuvants enhancing efficacy.
- Vaccine development involves preclinical studies, phased clinical trials (I-III), and regulatory approval processes.
- Passive immunity via maternal antibodies or monoclonal antibodies provides temporary protection in vulnerable populations.
- Postlicensure surveillance is essential to monitor vaccine safety, effectiveness, and address emerging challenges.
1. DEFINITION & OVERVIEW¶
Immunization is the process of inducing resistance to infectious diseases through vaccines. Vaccines are defined as inactivated/attenuated pathogens, their components (nucleic acids, proteins), or toxoids that stimulate protective immune responses. Adjuvants enhance immune responses by boosting antigen presentation and innate immune activation.
Table 128-1 Categories and Characteristics of Approved Vaccines and Adjuvants¶
| VACCINES | TECHNOLOGY | DESCRIPTION | EXAMPLES | ADVANTAGES | DISADVANTAG ES |
|---|---|---|---|---|---|
| Live attenuated | Weakened pathogen | Mimics natural infection | Measles, varicella | Durable immunity, single doses | Safety concerns in immunocompr omised |
| Inactivated | Nonreplicating pathogen/toxin | Induces broad immune response | Polio, hepatitis A | Large-scale production | Multiple doses needed |
| Purified protein-based | Specific pathogen components | Highly specific response | Influenza, pertussis | Noninfectious, low reactogenicity | May require adjuvants |
| Polysaccharide- protein conjugates | Polysaccharide + protein carrier | Strong immune response in infants | Pneumococcal, Hib | Conjugate provides cross-protection | Technically costly |
| Virus-like particles | Noninfectious protein structures | Broad immunity | Hepatitis B, HPV | Noninfectious | Difficult to produce |
| Replicating viral vectors | Nonpathogenic virus delivers antigen | High scalability | Ebola vaccine | Immunity to vector may interfere | Safety concerns in immunocompr omised |
| VACCINES | TECHNOLOGY | DESCRIPTION | EXAMPLES | ADVANTAGES | DISADVANTAG ES |
|---|---|---|---|---|---|
| Nonreplicating viral vectors | Replication-defic ient virus | Broad immune response | COVID-19 vaccines | High scalability | Immunity to vector may dampen response |
| Nucleic acid (DNA/RNA) | Lipid nanoparticles deliver genetic material | Rapid development | mRNA vaccines | Effective in most populations | Requires boosters |
Table 128-1 Adjuvants¶
| TECHNOLOGY | EXAMPLES | CURRENT USE | MECHANISM OF ACTION |
|---|---|---|---|
| Alum | Aluminum hydroxide/phosphate | HPV, DTaP | Depot effect, enhances antibody production |
| Oil-in-water emulsions | AS03, MF59 | Influenza vaccines | Enhance innate/adaptive immune responses |
| TLR agonists | MPL, CpG | HPV, hepatitis B | Activate TLR to enhance antigen presentation |
| Saponins | QS-21, Matrix-M | Malaria, RSV vaccines | Prolong antigen bioavailability |
| Delivery platforms | Lipid nanoparticles | mRNA vaccines | Improve lymphatic transport, antigen uptake |
1.1 Vaccine Types¶
Live attenuated vaccines (e.g., measles, varicella) mimic natural infection; inactivated vaccines (e.g., polio) use nonreplicating pathogens; subunit vaccines (e.g., hepatitis B) target specific antigens; nucleic acid vaccines (e.g., mRNA) use genetic material for antigen production.
1.2 Adjuvants¶
Adjuvants enhance immune responses by improving antigen uptake, activating innate immunity (e.g., TLR agonists), or creating depot effects (e.g., alum). Modern adjuvants include lipid nanoparticles (LNPs) for mRNA vaccines and saponin-based formulations (e.g., Matrix-M).
2. EPIDEMIOLOGY¶
Vaccination programs have reduced severe disease and mortality from infectious diseases. Global vaccination averted >37 million deaths (2000-2019). High-risk groups include older adults, immunocompromised, and those with comorbidities (diabetes, CVD, CKD).
2.1 Risk Factors¶
Age ≥ 65, obesity, diabetes, CVD, CKD, male sex, pregnancy, and immunocompromised states increase risk of severe outcomes from vaccine-preventable diseases.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Vaccines induce immune responses through antigen presentation, T-cell activation, and antibody production. Adjuvants enhance these responses by modulating innate immunity and antigen processing.
3.1 Immune Responses¶
Primary responses take weeks to develop, while secondary responses (booster doses) induce rapid antibody production. Memory cells sustain long-term immunity. mRNA vaccines use LNPs for in vivo antigen production.
4. CLINICAL FEATURES¶
Vaccine-preventable diseases present with fever, respiratory symptoms, or systemic complications. Severe cases may involve respiratory failure, sepsis, or multiorgan dysfunction. Passive immunity (maternal antibodies) provides temporary protection in neonates.
5. DIFFERENTIAL DIAGNOSIS¶
Acute febrile illnesses (e.g., influenza, dengue) must be differentiated from vaccine-related adverse events. Thrombocytopenia and rapid respiratory deterioration may distinguish viral syndromes from other infections.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis relies on clinical presentation, serologic testing, and molecular assays (PCR). For severe cases, imaging (chest X-ray/CT) and biomarkers (D-dimer, lactate) assess disease severity. Serologic correlates of protection (e.g., antibody levels) guide vaccine efficacy evaluation.
6.1 Diagnostic Criteria¶
Laboratory-confirmed disease with vaccine-directed pathogen. Serologic correlates (e.g., antibody titers) may replace clinical endpoints in some trials.
7. MANAGEMENT & TREATMENT¶
Supportive care, antivirals (nirmatrelvir/ritonavir, remdesivir), and corticosteroids (dexamethasone) reduce mortality in severe cases. Monoclonal antibodies (e.g., tocilizumab) may be used for cytokine storm. Passive immunization with monoclonal antibodies is used in high-risk populations.
8. PROGNOSIS & COMPLICATIONS¶
Mortality remains ≥ 20% in ICU patients with severe disease. Long-term complications include post-viral syndromes (e.g., long COVID). Postlicensure surveillance monitors vaccine safety and effectiveness.
9. SPECIAL CONSIDERATIONS¶
Maternal immunization protects neonates via transplacental antibodies. Vaccines for pregnant women (e.g., influenza, RSV) reduce maternal and fetal morbidity. Pediatric vaccines require age-appropriate formulations and dosing schedules.
9.1 Pregnancy¶
Influenza and RSV vaccines are recommended for pregnant women to prevent maternal-fetal complications. Live vaccines are contraindicated, but inactivated vaccines are safe.
10. KEY POINTS & CLINICAL PEARLS¶
Vaccination is the most effective strategy to prevent infectious diseases. Adjuvants enhance immune responses but require careful risk-benefit assessment. Postlicensure surveillance is critical to monitor vaccine safety and address emerging threats. Passive immunization with monoclonal antibodies is used in high-risk populations.