Pharmacology of Vaccines and Sera

1. Introduction/Overview

The pharmacological management of infectious diseases extends beyond antimicrobial agents to include biological products designed to induce or provide immunity. Vaccines and immune sera represent two fundamental, yet pharmacologically distinct, approaches to prophylaxis and therapy. Vaccines are immunobiological substances administered to elicit an active, adaptive immune response and establish immunological memory, thereby preventing future infection. In contrast, immune sera, including antitoxins and immunoglobulins, provide passive immunity through the direct administration of pre-formed antibodies, offering immediate but temporary protection or treatment. The clinical importance of these agents is profound, underpinning global public health initiatives that have led to the eradication of smallpox, the near-elimination of poliomyelitis, and significant reductions in morbidity and mortality from numerous other pathogens. Their role extends from routine childhood immunization to post-exposure prophylaxis, outbreak control, and the management of specific intoxications.

Learning Objectives

• Differentiate the fundamental pharmacological principles underlying active immunization (vaccines) and passive immunization (immune sera).
• Explain the mechanisms of action for major vaccine platforms (e.g., live attenuated, inactivated, subunit, mRNA) and the various types of immune sera.
• Describe the unique pharmacokinetic and pharmacodynamic properties of vaccines and sera, including factors influencing immune response kinetics and duration.
• Identify the major therapeutic applications, adverse effect profiles, and contraindications for commonly used vaccines and immune sera.
• Apply knowledge of special considerations, including use in immunocompromised hosts, pregnancy, and specific clinical scenarios such as post-exposure prophylaxis.

2. Classification

Vaccines and sera are classified based on their composition, origin, and mechanism of conferring immunity. This classification informs their clinical use, storage requirements, and safety profiles.

Classification of Vaccines

Vaccines are primarily categorized by the nature of the antigenic material presented to the immune system.

• Live Attenuated Vaccines: Contain whole pathogens that have been weakened (attenuated) under laboratory conditions to lose pathogenicity while retaining immunogenicity. Examples include vaccines against measles, mumps, rubella (MMR), varicella, and oral poliovirus (OPV). They typically induce robust and durable cellular and humoral immunity.
• Inactivated Vaccines: Contain pathogens that have been killed or inactivated by chemical (e.g., formaldehyde) or physical (e.g., heat) means. Examples include inactivated poliovirus (IPV), whole-cell pertussis, hepatitis A, and rabies vaccines. They are generally less immunogenic than live vaccines and often require adjuvants and multiple doses.
• Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: These vaccines utilize specific, isolated components of a pathogen rather than the whole organism.
  • Protein Subunit/Recombinant: Contain purified antigenic proteins (e.g., hepatitis B surface antigen, acellular pertussis components).
  • Polysaccharide: Contain long chains of sugar molecules that make up the capsule of certain bacteria (e.g., pneumococcal polysaccharide vaccine, meningococcal polysaccharide vaccine). These are often poorly immunogenic in young children.
  • Conjugate: Polysaccharides chemically linked to a carrier protein (e.g., tetanus toxoid), which enhances immunogenicity and induces T-cell dependent memory. Examples include Haemophilus influenzae type b (Hib), pneumococcal conjugate, and meningococcal conjugate vaccines.
• Nucleic Acid Vaccines (mRNA/DNA): Utilize genetic material (messenger RNA or plasmid DNA) that encodes for a pathogen-specific antigen. Host cells take up this genetic material and produce the antigen, which then stimulates an immune response. mRNA vaccines against SARS-CoV-2 are prominent examples.
• Viral Vector Vaccines: Use a modified, non-replicating or replicating virus (the vector) to deliver genetic code for a pathogen antigen into host cells. Examples include certain Ebola and SARS-CoV-2 vaccines.
• Toxoid Vaccines: Contain bacterial exotoxins that have been inactivated (toxoided) to eliminate toxicity while retaining antigenicity. Examples include tetanus and diphtheria toxoids.

Classification of Immune Sera

Immune sera are classified based on their source and specificity.

• Homologous (Human) Sera: Derived from the pooled plasma of human donors with high antibody titers. Examples include:
  • Human Tetanus Immune Globulin (HTIG)
  • Hepatitis B Immune Globulin (HBIG)
  • Varicella-Zoster Immune Globulin (VZIG)
  • Intravenous Immune Globulin (IVIG) – for broad-spectrum passive immunity.

  These generally have a longer half-life (approximately 3-4 weeks) and lower risk of serum sickness compared to heterologous sera.

• Heterologous (Animal) Sera/Antitoxins: Derived from the plasma of immunized animals, typically horses. These are antitoxins that neutralize specific bacterial toxins. Examples include:
  • Diphtheria Antitoxin
  • Botulism Antitoxin
  • Snake and Spider Antivenins

  Their use carries a significant risk of hypersensitivity reactions, including anaphylaxis and serum sickness.

• Monoclonal Antibodies (mAbs): Although not traditionally termed “sera,” these represent a modern form of highly specific passive immunity. They are laboratory-produced molecules engineered to bind to a single epitope. Examples include palivizumab for respiratory syncytial virus (RSV) prophylaxis and casirivimab/imdevimab (for SARS-CoV-2, though use varies).

3. Mechanism of Action

The pharmacodynamic principles of vaccines and sera are rooted in immunology, but their mechanisms differ fundamentally in the engagement of the adaptive immune system.

Pharmacodynamics of Vaccines (Active Immunization)

Vaccines function as artificial, controlled immunogens. Their administration mimics a natural infection, initiating the innate immune response and, crucially, priming the adaptive immune system without causing disease. The mechanism involves a coordinated sequence:

1. Antigen Presentation and Innate Immune Activation: Upon administration, vaccine antigens, along with any adjuvants, are taken up by antigen-presenting cells (APCs), primarily dendritic cells, at the site of injection. Adjuvants (e.g., aluminum salts, MF59, AS01_B) act as “danger signals,” stimulating pattern recognition receptors (PRRs) on APCs. This activation promotes APC maturation, characterized by increased expression of major histocompatibility complex (MHC) molecules and co-stimulatory signals (e.g., CD80/86), and migration to draining lymph nodes.
2. Activation of Naïve T and B Lymphocytes: In the lymph node, processed antigen peptides presented on MHC class II molecules activate CD4+ T-helper (T_H) cells. The cytokine milieu determines the T_H subset differentiation (e.g., T_H1, T_H2, T_H17, T_FH), shaping the character of the immune response. For protein antigens, B cells can also directly recognize native antigen via their surface immunoglobulin (B cell receptor).
3. Clonal Expansion and Differentiation: Activated T_H cells, particularly T follicular helper (T_FH) cells, provide critical help to B cells in the germinal center reaction. This leads to B cell clonal expansion, somatic hypermutation, affinity maturation, and differentiation into either:
   • Plasma Cells: Antibody-secreting effector cells that produce antigen-specific immunoglobulins (IgM initially, then IgG, IgA).
   • Memory B Cells: Long-lived cells that persist and can rapidly differentiate into plasma cells upon re-exposure to the antigen.

   Concurrently, CD8+ T cells are activated by antigens presented on MHC class I (relevant for live attenuated, viral vector, and nucleic acid vaccines), leading to the generation of cytotoxic T lymphocytes (CTLs) and memory T cells.

4. Establishment of Immunological Memory: The generation of memory B cells, memory T cells, and long-lived plasma cells (which may reside in the bone marrow) constitutes immunological memory. This enables a more rapid, robust, and effective secondary immune response upon encountering the wild-type pathogen, thereby preventing or attenuating clinical disease.

The specific characteristics of the vaccine platform influence this process. Live attenuated vaccines often induce the most comprehensive immunity, including strong CTL responses, as they undergo limited replication. mRNA vaccines are efficiently translated in host cell cytoplasm, with antigens presented via both MHC class I and II pathways, inducing balanced humoral and cellular responses.

Pharmacodynamics of Immune Sera (Passive Immunization)

Immune sera bypass the need for host immune system activation. Their mechanism is direct and immediate, based on the principles of antibody function:

• Neutralization: The primary mechanism. Antibodies bind to critical epitopes on pathogens (e.g., viral attachment proteins) or toxins, physically blocking their interaction with host cellular receptors. This prevents viral entry into cells or toxin binding to target tissues.
• Opsonization: Antibodies (particularly IgG) coat the pathogen, with their Fc region recognized by Fc receptors on phagocytic cells (neutrophils, macrophages), enhancing phagocytosis and clearance.
• Complement Activation: The antibody-antigen complex can activate the classical complement pathway, leading to opsonization (via C3b), recruitment of inflammatory cells, and direct lysis of enveloped pathogens (via the membrane attack complex).
• Antibody-Dependent Cellular Cytotoxicity (ADCC): The Fc region of antibodies bound to infected host cells can engage Fc receptors on natural killer (NK) cells, triggering the release of cytotoxic granules that kill the infected cell.

Passive immunization provides immediate protection but is transient, as the administered antibodies are gradually catabolized and no immunological memory is established. The specificity is determined by the donor pool (for polyclonal sera) or the engineered target (for monoclonal antibodies).

4. Pharmacokinetics

The pharmacokinetic profiles of vaccines and sera are atypical compared to small-molecule drugs, as their “active ingredients” are complex biological molecules or entire microorganisms, and their primary effect is the induction or provision of an immune response.

Vaccine Pharmacokinetics

The classical ADME model is less applicable; the critical parameters relate to the kinetics of the immune response rather than the concentration of the vaccine antigen in plasma.

• Absorption: Most vaccines are administered via intramuscular or subcutaneous injection, with absorption of the antigenic material and adjuvant from the depot site. The rate and extent of antigen dispersal and uptake by APCs are influenced by formulation, presence of adjuvants, and injection technique. Intranasal (live attenuated influenza) and oral (oral polio, rotavirus) vaccines are absorbed across mucosal surfaces.
• Distribution: Distribution is typically local and regional. Antigens and activated APCs travel via lymphatic drainage to regional lymph nodes, the primary site of immune activation. Systemic distribution of the vaccine antigen itself is usually minimal and not clinically relevant, though some components (e.g., mRNA in lipid nanoparticles) may have wider tissue distribution.
• Metabolism and Elimination: Vaccine antigens are processed and degraded via normal proteolytic pathways within APCs and other cells. Adjuvants and excipients are metabolized or eliminated through standard physiological routes. The vaccine components themselves are not excreted as intact entities.
• Immune Response Kinetics:

  The clinically relevant “pharmacokinetic” measures are immunologic:

  • Onset: Detectable antibody titers (seroconversion) typically appear 7-14 days after primary vaccination, with peak titers reached within weeks to a few months.
  • Half-life of the Immune Response: Following the peak, antibody titers decline with an initial rapid phase (loss of short-lived plasma cells) followed by a slow, persistent phase maintained by long-lived plasma cells and memory B cells. The functional half-life of vaccine-induced IgG antibodies varies significantly, from several years (e.g., measles) to months (e.g., inactivated influenza), necessitating booster doses.
  • Factors Influencing Response: The magnitude and duration of the immune response depend on vaccine factors (platform, antigen dose, adjuvant, number of doses, interval between doses) and host factors (age, genetics, nutritional status, co-morbidities, immunosuppression).

  Pharmacokinetics of Immune Sera

  The pharmacokinetics of immunoglobulins follow predictable patterns based on their protein nature.

  • Absorption: When administered intramuscularly, IgG absorption is slow and incomplete, with peak serum levels achieved in 2-7 days. Intravenous administration provides immediate and complete bioavailability, achieving peak serum levels at the end of the infusion.
  • Distribution: IgG distributes primarily within the intravascular and extravascular fluid compartments. The volume of distribution for IgG is approximately equal to the plasma volume (∼0.05 L/kg) initially but increases as equilibrium is reached between vascular and extravascular spaces.
  • Metabolism and Elimination: Immunoglobulins are catabolized by proteolytic enzymes throughout the body, primarily in the reticuloendothelial system. They are not excreted renally as intact molecules. The elimination half-life is determined by the Fc region’s interaction with the neonatal Fc receptor (FcRn), which protects IgG from degradation. The half-life of human IgG is approximately 21-28 days. Heterologous (animal) IgG typically has a shorter half-life (∼5-7 days) due to more rapid immune clearance.
  • Dosing Considerations: Dosing is based on the desired serum titer of neutralizing antibody and the estimated volume of distribution. For prophylaxis, a dose is calculated to achieve a protective titer for the expected duration of risk, considering the agent’s half-life. For treatment of ongoing infection or intoxication, larger loading doses may be required to neutralize a high antigen load.

  5. Therapeutic Uses/Clinical Applications

  The applications of vaccines and sera span routine prevention, outbreak control, post-exposure management, and specific therapeutic interventions.

  Therapeutic Uses of Vaccines

  • Routine Immunization: The cornerstone of preventive medicine. National schedules (e.g., by CDC’s ACIP or WHO) outline the administration of vaccines from infancy through adulthood against diseases such as diphtheria, tetanus, pertussis, polio, Haemophilus influenzae type b, hepatitis B, pneumococcal disease, rotavirus, measles, mumps, rubella, varicella, human papillomavirus (HPV), and meningococcal disease.
  • Seasonal and Pandemic Vaccination: Annual inactivated or live attenuated influenza vaccines are recommended. Vaccines developed rapidly during pandemics (e.g., H1N1 influenza, SARS-CoV-2) are critical for curbing transmission and severe disease.
  • Travel Medicine: Vaccination against yellow fever, typhoid, Japanese encephalitis, cholera, and rabies (pre-exposure) is indicated for travelers to endemic regions.
  • Occupational Health: Vaccination for healthcare workers (influenza, hepatitis B, MMR, varicella), laboratory personnel (e.g., anthrax), and veterinarians (rabies).
  • Post-Exposure Prophylaxis: Certain vaccines are effective even after exposure if administered promptly. Key examples include rabies vaccine, varicella vaccine, and measles vaccine.
  • Special Populations: High-risk groups receive specific recommendations, such as pneumococcal and influenza vaccines for the elderly and immunocompromised, and Tdap during each pregnancy to protect the newborn from pertussis.

  Therapeutic Uses of Immune Sera

  • Post-Exposure Prophylaxis (PEP): To prevent disease after known or suspected exposure to a pathogen or toxin.
    • Tetanus: Tetanus Immune Globulin (TIG) for wound management in inadequately immunized individuals.
    • Rabies: Rabies Immune Globulin (RIG) infiltrated around the wound site, combined with rabies vaccine.
    • Hepatitis B: HBIG for perinatal exposure of infants born to HBsAg-positive mothers or after needlestick injuries.
    • Varicella: Varicella-Zoster Immune Globulin (VZIG) for susceptible, high-risk individuals (e.g., immunocompromised, newborns) exposed to varicella.
  • Treatment of Disease or Intoxication:
    • Diphtheria/Botulism: Specific antitoxin to neutralize circulating toxin. Administration must occur early before toxin binds irreversibly to tissues.
    • Snake/Spider Envenomation: Species-specific antivenom to neutralize venom toxins.
    • Immunodeficiency: Intravenous Immune Globulin (IVIG) for antibody deficiency disorders (e.g., X-linked agammaglobulinemia) to prevent recurrent infections.
    • Specific Infections: Cytomegalovirus Immune Globulin (CMV-IG) in transplant recipients, RSV monoclonal antibody (palivizumab) for high-risk infants.
  • Immunomodulation: High-dose IVIG is used for autoimmune and inflammatory conditions (e.g., immune thrombocytopenic purpura, Kawasaki disease, Guillain-Barré syndrome) via mechanisms involving Fc receptor blockade, anti-idiotypic antibody effects, and modulation of cytokine production.

  6. Adverse Effects

  Adverse effects range from common, mild local reactions to rare, severe systemic events. The benefit-risk profile overwhelmingly favors vaccination, but vigilant monitoring and reporting are essential.

  Vaccine Adverse Effects

  • Local Reactions: Pain, erythema, swelling, and induration at the injection site are the most common adverse effects, often related to the inflammatory response triggered by the antigen and adjuvant. These are typically self-limiting, resolving within 24-72 hours.
  • Systemic Reactions: Low-grade fever, malaise, myalgia, headache, and irritability. These are also common, short-lived, and reflect the systemic immune activation. They are more frequent with some vaccines (e.g., live attenuated vaccines, adjuvanted influenza vaccines) and after booster doses.
  • Allergic Reactions: Immediate hypersensitivity (Type I) reactions, including anaphylaxis, are rare but serious. Potential allergens include vaccine antigens themselves, residual animal proteins (e.g., egg protein in influenza and yellow fever vaccines grown in eggs), gelatin stabilizers, antibiotics (e.g., neomycin, streptomycin), or latex in vial stoppers/syringes.
  • Specific Vaccine-Associated Risks:
    • Live Attenuated Vaccines: Can cause mild, vaccine-strain disease in immunocompetent hosts (e.g., rash after varicella vaccine) and severe, disseminated disease in severely immunocompromised individuals. They are generally contraindicated in pregnancy due to theoretical risk to the fetus.
    • MMR Vaccine: Associated with febrile seizures 6-12 days post-vaccination. A causal relationship with autism has been thoroughly investigated and definitively disproven.
    • Rotavirus Vaccine: A very small increased risk of intussusception.
    • HPV Vaccine: Commonly associated with syncope, related to the vaccination process rather than the vaccine itself; observation for 15 minutes post-vaccination is recommended.
    • COVID-19 mRNA Vaccines: Associated with a very rare risk of myocarditis/pericarditis, primarily in adolescent and young adult males, and anaphylaxis (∼5 per million doses). Thrombosis with thrombocytopenia syndrome (TTS) is a rare event associated with adenovirus-vector COVID-19 vaccines.
  • Autoimmune/Neurological Events: Conditions like Guillain-Barré Syndrome (GBS) have been temporally associated with some vaccines (e.g., 1976 swine flu vaccine, influenza vaccines at a very low excess risk of ∼1-2 cases per million). The attributable risk is extremely low and often lower than the risk following natural infection.

  Adverse Effects of Immune Sera

  • Hypersensitivity Reactions: The most significant concern, particularly with heterologous (animal-derived) sera.
    • Anaphylaxis (Type I): An immediate, IgE-mediated reaction that can occur within minutes to hours, especially in individuals with prior exposure to the animal protein.
    • Serum Sickness (Type III): A delayed reaction occurring 7-14 days after administration. It results from the formation of immune complexes between the foreign protein and host antibodies, leading to fever, arthralgia, lymphadenopathy, and urticarial rash.

    Skin testing is often performed prior to administering heterologous sera, though it has limited predictive value.

  • Local Reactions: Pain and tenderness at the injection site for intramuscular preparations.
  • Systemic Reactions: Fever, chills, headache, nausea, and flushing, particularly with rapid intravenous infusion of immunoglobulins.
  • IVIG-Specific Reactions:
    • Aseptic Meningitis: A severe headache with meningeal signs, occurring hours to days after infusion, likely related to cytokine release.
    • Thromboembolic Events: High-osmolarity or rapid infusion can increase blood viscosity, posing a risk in patients with pre-existing risk factors.
    • Hemolytic Anemia: Due to anti-A/anti-B isohemagglutinins in some IVIG preparations, particularly with high doses.
    • Renal Dysfunction: Historically associated with sucrose-stabilized products causing osmotic nephrosis; less common with current formulations.

  7. Drug Interactions

  Interactions primarily involve immunological interference or the effects of concomitant therapies on vaccine efficacy and safety.

  Vaccine Drug Interactions

  • Immunosuppressive Agents: Corticosteroids (at high doses, e.g., ≥20 mg/day prednisone equivalent for ≥2 weeks), chemotherapy, radiation therapy, and biologic immunomodulators (e.g., anti-TNF agents, rituximab) can diminish the immune response to vaccines. Live vaccines are generally contraindicated due to the risk of uncontrolled replication. Inactivated vaccines are safe but may be less effective; timing administration before immunosuppression or during periods of minimal immunosuppression is advised.
  • Anticoagulants: Intramuscular vaccination in patients on therapeutic anticoagulation carries a risk of hematoma. Subcutaneous administration may be preferred, or vaccination should be scheduled in consultation with the managing physician.
  • Other Vaccines: Most inactivated vaccines can be administered simultaneously at different anatomical sites without interference. Live virus vaccines not given on the same day should be spaced at least 28 days apart to minimize potential interference from the antiviral immune response elicited by the first vaccine.
  • Antiviral Medications: Antiviral drugs active against the vaccine virus (e.g., acyclovir) may inhibit the replication of live attenuated vaccines (e.g., varicella zoster vaccine), potentially reducing efficacy. These drugs are typically withheld for a period before and after vaccination.
  • Blood Products and IVIG: Passively acquired antibodies from blood transfusions or IVIG can interfere with the immune response to live attenuated vaccines (particularly measles and varicella). Vaccination should be deferred for a period (typically 3-11 months, depending on the dose of IVIG) after receipt of these products.

  Immune Sera Drug Interactions

  • Live Vaccines: As noted, administration of immune sera (especially IVIG) can interfere with the response to live attenuated vaccines. The recommended interval between receiving immune sera and a live vaccine varies from 3 to 11 months.
  • Other Blood-Derived Products: Caution is exercised when administering multiple blood products due to the cumulative risk of volume overload, transfusion reactions, and hyperproteinemia.
  • Vaccines for Post-Exposure Prophylaxis: When immune serum and a vaccine are used together (e.g., rabies IG with rabies vaccine, tetanus IG with tetanus toxoid), they must be administered at separate anatomical sites using separate syringes to prevent antibody neutralization of the vaccine antigen at the injection site.

  Contraindications

  • Vaccines: Severe allergic reaction (e.g., anaphylaxis) to a prior dose of the vaccine or to any of its components is an absolute contraindication. For live attenuated vaccines, additional contraindications include pregnancy, severe immunodeficiency (e.g., from HIV with low CD4 count, leukemia, lymphoma, therapy with high-dose steroids, alkylating agents, antimetabolites, radiation, or TNF blockers). A history of intussusception is a contraindication for rotavirus vaccine.
  • Immune Sera: Known severe hypersensitivity (anaphylaxis) to the product or its components is a contraindication. For heterologous sera, a history of prior reaction may be a relative contraindication, necessitating desensitization protocols if use is essential.

  8. Special Considerations

  Pregnancy and Lactation

  Vaccines: Inactivated vaccines (e.g., Tdap, inactivated influenza, hepatitis B, COVID-19 mRNA vaccines) are recommended when indicated during pregnancy, as they pose no risk to the fetus and protect both mother and infant. Live attenuated vaccines (e.g., MMR, varicella) are contraindicated due to theoretical risk of fetal infection, though termination of pregnancy is not recommended if inadvertently given. Vaccination during lactation is safe for all vaccines.

  Immune Sera: Most immune sera (e.g., TIG, HBIG, IVIG) can be administered during pregnancy and lactation if clearly needed. The benefits of preventing a serious disease like tetanus or rabies outweigh potential risks. Animal-derived antitoxins may be used in life-threatening situations.

  Pediatric and Geriatric Considerations

  Pediatrics: Immunization schedules are designed based on the maturation of the infant immune system and the epidemiology of disease. Preterm infants should be vaccinated according to their chronological age. Dose volumes are not adjusted by weight for standard pediatric vaccines. Conjugate vaccines are crucial for young children who respond poorly to plain polysaccharides.

  Geriatrics: Immunosenescence—the age-related decline in immune function—leads to diminished humoral and cellular responses to vaccines. Higher antigen doses (e.g., high-dose influenza vaccine) or adjuvanted formulations (e.g., adjuvanted influenza vaccine, recombinant zoster vaccine with AS01_B adjuvant) are often recommended to enhance immunogenicity and protection in older adults.

  Renal and Hepatic Impairment

  Renal Impairment: No dose adjustment is required for vaccines. Patients with advanced chronic kidney disease or on dialysis are at increased risk for infections and are prioritized for vaccination (e.g., pneumococcal, hepatitis B, influenza). For IVIG, caution is advised in patients with renal dysfunction; using products with lower osmolarity and ensuring adequate hydration can mitigate the risk of renal injury.

  Hepatic Impairment: No specific dose adjustments for vaccines or immune sera are required. However, patients with chronic liver disease (e.g., cirrhosis) are at high risk for severe outcomes from infections like hepatitis A, hepatitis B, and pneumococcal disease, making vaccination particularly important.

  Immunocompromised Hosts

  This is a critical consideration. Inactivated vaccines are safe but may have suboptimal efficacy. Live vaccines are generally contraindicated, except in specific scenarios (e.g., MMR and varicella may be considered for HIV-infected children with adequate CD4 counts). The timing of vaccination relative to immunosuppressive therapy (e.g., before transplant or between chemotherapy cycles) is crucial. Close contacts of immunocompromised individuals should be up-to-date with their vaccinations to provide indirect protection (cocooning).

  9. Summary/Key Points

  • Vaccines induce active, long-term immunity by priming the adaptive immune system, while immune sera provide immediate, short-term passive immunity through pre-formed antibodies.
  • Vaccines are classified by platform (live attenuated, inactivated, subunit, nucleic acid, etc.), which determines their immunogenicity, safety profile, and storage requirements. Immune sera are classified by source (homologous/human or heterologous/animal) and specificity.
  • The mechanism of action for vaccines involves antigen presentation, lymphocyte activation, and the establishment of immunological memory. Immune sera work primarily through direct neutralization of pathogens or toxins.
  • The pharmacokinetics of vaccines are best described by the kinetics of the immune response (seroconversion, antibody decay). Immune sera follow typical protein pharmacokinetics, with a half-life of ∼3-4 weeks for human IgG.
  • Vaccines are used for routine prevention, travel, and post-exposure prophylaxis. Immune sera are used for post-exposure prophylaxis, treatment of specific intoxications/infections, and immunomodulation.
  • Common vaccine adverse effects are local and systemic reactogenicity. Serious risks (e.g., anaphylaxis, specific associations like myocarditis) are rare. Immune sera carry risks of hypersensitivity reactions, including anaphylaxis and serum sickness, especially with animal-derived products.
  • Major interactions involve immunosuppressive drugs (which reduce vaccine efficacy and contraindicate live vaccines) and the interference of passively acquired antibodies (from sera or blood products) with live vaccine responses.
  • Special populations require tailored approaches: inactivated vaccines are recommended in pregnancy; live vaccines are contraindicated. Geriatric patients benefit from enhanced vaccines. Immunocompromised hosts require careful vaccine selection and timing.

  Clinical Pearls

  • When managing a tetanus-prone wound in a patient with unknown or incomplete vaccination history, both tetanus toxoid (active immunization) and tetanus immune globulin (passive immunization) should be administered at separate sites.
  • For post-exposure rabies prophylaxis, rabies immune globulin (RIG) should be infiltrated around the wound site to neutralize virus locally, while the rabies vaccine series is initiated in a different limb to induce active immunity.
  • In patients about to start potent immunosuppressive therapy (e.g., rituximab), administer necessary vaccines at least 2-4 weeks prior to therapy to maximize the immune response.
  • Anaphylaxis following vaccination is a medical emergency but is exceedingly rare (∼1 per million doses). Vaccination clinics must have epinephrine and protocols for managing acute allergic reactions readily available.
  • The contraindication to live vaccines in immunocompromised patients is relative to the degree of immunosuppression. Guidelines exist for specific conditions (e.g., HIV) where vaccination may be permissible if immune function is adequately preserved.

  References

  1. Rang HP, Ritter JM, Flower RJ, Henderson G. Rang & Dale's Pharmacology. 9th ed. Edinburgh: Elsevier; 2020.
  2. Whalen K, Finkel R, Panavelil TA. Lippincott Illustrated Reviews: Pharmacology. 7th ed. Philadelphia: Wolters Kluwer; 2019.
  3. Golan DE, Armstrong EJ, Armstrong AW. Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. 4th ed. Philadelphia: Wolters Kluwer; 2017.
  4. Trevor AJ, Katzung BG, Kruidering-Hall M. Katzung & Trevor's Pharmacology: Examination & Board Review. 13th ed. New York: McGraw-Hill Education; 2022.
  5. Katzung BG, Vanderah TW. Basic & Clinical Pharmacology. 15th ed. New York: McGraw-Hill Education; 2021.
  6. Brunton LL, Hilal-Dandan R, Knollmann BC. Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed. New York: McGraw-Hill Education; 2023.
  7. Rang HP, Ritter JM, Flower RJ, Henderson G. Rang & Dale's Pharmacology. 9th ed. Edinburgh: Elsevier; 2020.
  8. Whalen K, Finkel R, Panavelil TA. Lippincott Illustrated Reviews: Pharmacology. 7th ed. Philadelphia: Wolters Kluwer; 2019.

  ⚠️ Medical Disclaimer

  This article is intended for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read in this article.

  The information provided here is based on current scientific literature and established pharmacological principles. However, medical knowledge evolves continuously, and individual patient responses to medications may vary. Healthcare professionals should always use their clinical judgment when applying this information to patient care.

  How to cite this page - Vancouver Style

  Mentor, Pharmacology. Pharmacology of Vaccines and Sera. Pharmacology Mentor. Available from: https://pharmacologymentor.com/pharmacology-of-vaccines-and-sera/. Accessed on February 2, 2026 at 17:45.
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