Unit
- Adaptive immunity: Vaccination stimulates the adaptive immune system by introducing antigens that trigger B and T cell responses. Memory cells persist for years, providing long-term protection against specific pathogens without causing disease.
- Humoral vs. cell-mediated responses: B cells produce antibodies that neutralize extracellular pathogens, while T cells eliminate infected cells. Most adult vaccines induce both arms, though polysaccharide vaccines primarily elicit humoral responses.
- Antigen presentation: Dendritic cells capture vaccine antigens and present them to naive T cells in lymph nodes. This initiates a cascade leading to clonal expansion and effector cell differentiation.
- Immunologic memory: After primary vaccination, memory B and T cells remain in circulation. Upon re-exposure, these cells rapidly proliferate, producing a faster and stronger secondary response that prevents clinical infection.
- Herd immunity threshold: When vaccination rates exceed a critical level (typically 90-95% for measles), transmission chains are interrupted, protecting those who cannot be vaccinated due to medical contraindications.
- Vaccine types used in adults: Inactivated vaccines (e.g., influenza shot), live attenuated vaccines (e.g., MMR, varicella), subunit/recombinant vaccines (e.g., hepatitis B), and mRNA vaccines (e.g., COVID-19). Each type induces distinct immune pathways.
- Adjuvants and their role: Aluminum salts, MF59, and AS01 enhance immune response by prolonging antigen exposure or activating innate immunity. Adjuvanted vaccines often require fewer doses or produce higher antibody titers.
- Booster doses: For some vaccines (e.g., tetanus/diphtheria, pertussis), immune waning requires periodic boosters to maintain protective antibody levels. The interval varies by vaccine and patient age.
- Correlates of protection: For many vaccines, specific antibody titers are known to correlate with clinical efficacy. Serologic testing can confirm immunity when documentation is missing.
- Primary vs. secondary vaccine failure: Primary vaccine failure occurs when an individual does not mount a protective immune response after vaccination. Secondary failure involves waning immunity over time. Recognizing this distinction helps clinicians interpret breakthrough infections and determine when a booster dose is indicated for an adult patient.
- Mucosal immunity and vaccines: Many respiratory and enteric pathogens initially infect mucosal surfaces. Vaccines such as the intranasal live attenuated influenza vaccine are formulated to induce mucosal IgA antibodies and resident memory T cells, providing a frontline defense distinct from systemic immunity.
- Contraindications vs. precautions: A contraindication is a condition in a recipient that greatly increases the risk of a serious adverse event, such as anaphylaxis to a vaccine component. A precaution is a condition that might increase the risk of a reaction or diminish immune response, such as moderate or severe acute illness. Correct assessment is vital for safe administration.
- Combination vaccines for adults: Combination vaccines like Tdap (tetanus, diphtheria, pertussis) reduce the number of injections needed for adult catch-up schedules. They improve patient compliance and streamline clinical workflows without compromising immunogenicity or safety compared to separate component administration.
- The Advisory Committee on Immunization Practices (ACIP): The ACIP provides expert guidance on the use of vaccines for the U.S. civilian population. Their evidence-based recommendations establish the standard of care for adult immunization, defining age groups, risk factors, dosing schedules, and contraindications.
- Vaccine storage and handling: Maintaining the cold chain (2 to 8 degrees Celsius) for most adult vaccines is essential to preserve potency. Practices include using temperature monitored units, properly managing multidose vials, and following emergency protocols for power outages or equipment failures.
- Vaccinating special populations: Immunocompromised adults, including those with HIV, cancer, or on immunosuppressive therapies, require careful vaccine selection. Live vaccines are generally avoided, while inactivated vaccines may be given, though immune responses can be suboptimal. Timing vaccinations relative to therapy is critical.
Terminology
- Antigen
- A substance (e.g., protein, polysaccharide) that the immune system recognizes as foreign and mounts a response against.
- Antibody
- A protein produced by B cells that binds specifically to an antigen to neutralize or mark it for destruction.
- Adjuvant
- An ingredient added to a vaccine to enhance the immune response, allowing for lower antigen doses or fewer doses.
- Immunologic memory
- The ability of the immune system to recall a prior antigen encounter and respond more rapidly upon re-exposure.
Quick Revision
- Vaccination leverages adaptive immunity to create long-lasting memory B and T cells.
- Herd immunity protects vulnerable populations when vaccination coverage is high.
- Adult vaccines include inactivated, live attenuated, subunit, and mRNA platforms.
- Adjuvants boost immunogenicity; some vaccines require periodic boosters.