15.2 Public Health, Disease Reporting, and Adult Immunization Strategies

Public Health, Disease Reporting, and Adult Immunization Strategies

Infectious diseases pharmacy practice operates at the intersection of individual patient pharmacotherapy and population-level public health. Clinical pharmacists playing leadership roles in infectious diseases must master the principles of disease transmission dynamics, legal mandates governing public health surveillance and mandatory case notification, and the complex, rapidly evolving landscape of adult immunizations formulated by the Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP).

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Infectious Disease Epidemiology and Population Metrics

Epidemiology provides the quantitative scientific foundation for disease surveillance, outbreak containment, and population immunization targets.

1. Incidence, Prevalence, and Attack Rates

• Incidence: Quantifies the occurrence of new cases of disease arising in a population initially at risk during a specified observation interval.
  • Incidence Rate (Incidence Density): Incorporates person-time in the denominator, accounting for varying follow-up periods: $\text{Incidence Rate} = \frac{\text{Number of new cases during time period}}{\text{Total person-time at risk}}$.
  • Cumulative Incidence (Incidence Proportion): Measures the proportion of an initially disease-free cohort that develops disease over a set period: $\text{Cumulative Incidence} = \frac{\text{New cases during period}}{\text{Population at risk at baseline}}$.
• Prevalence: Quantifies the total existing burden of disease (both newly diagnosed and long-standing active cases) in a defined population at a designated time point.
  • Point Prevalence: $\text{Prevalence} = \frac{\text{Number of existing cases at specific time}}{\text{Total population at that specific time}}$.
  • Relationship to Incidence: Under steady-state conditions, $\text{Prevalence} \approx \text{Incidence} \times \text{Mean Duration of Disease}$. Interventions that cure infection rapidly (e.g., direct-acting antivirals for Hepatitis C) reduce prevalence without altering immediate incidence; conversely, interventions that prolong survival without cure (e.g., antiretroviral therapy for HIV) substantially increase prevalence.
• Attack Rate: A specialized form of cumulative incidence utilized specifically during acute epidemic outbreaks (e.g., foodborne gastroenteritis, acute nosocomial outbreaks). It calculates the proportion of exposed individuals who develop symptoms: $\text{Attack Rate} = \frac{\text{Number of ill exposed individuals}}{\text{Total number of exposed individuals}}$.

2. Basic Reproduction Number ($R_0$) and Herd Immunity Threshold

The Basic Reproduction Number ($R_0$) defines the average number of secondary infectious cases generated by a single primary infectious individual introduced into a completely susceptible, non-immune population under natural conditions.

• Epidemiological Interpretation:
  • $R_0 > 1$: The infection has epidemic potential and will spread through the population.
  • $R_0 = 1$: The infection remains stable and endemic in the population.
  • $R_0 < 1$: Transmission cannot sustain itself; the outbreak will decline and extinguish.
• Effective Reproduction Number ($R_t$ or $R$): Reflects transmission in a real-world, partially immune population (via vaccination or prior infection) where a fraction $s$ remains susceptible: $R_t = R_0 \times s$.
• Herd Immunity Threshold ($HIT$): The critical fraction of the population that must possess protective immunity (via vaccination or natural infection) to reduce $R_t$ below 1, thereby halting sustained community transmission:

$HIT = 1 - \frac{1}{R_0}$

                     HERD IMMUNITY DYNAMICS ACROSS PATHOGENS

  Pathogen        Basic Reproduction Number (R0)      Herd Immunity Threshold (HIT)
  ──────────────  ──────────────────────────────      ─────────────────────────────
  Influenza       1.3 – 1.8   ├───►                   23% – 44%
  Polio           5.0 – 7.0   ├─────────────►         80% – 86%
  Rubella         6.0 – 7.0   ├─────────────►         83% – 86%
  Pertussis       12.0 – 17.0 ├─────────────────────► 92% – 94%
  Measles         12.0 – 18.0 ├─────────────────────► 92% – 95%
                  0           5          10         15        20

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Public Health Surveillance and Mandatory Disease Reporting

Public health surveillance constitutes the ongoing, systematic collection, analysis, and interpretation of health data essential for public health planning, implementation, and evaluation.

Legal Framework and the NNDSS

In the United States, public health authority is constitutionally reserved to state and territorial governments under the Tenth Amendment. Mandatory disease reporting is therefore governed by state statutory laws and administrative codes, not federal law.

• National Notifiable Diseases Surveillance System (NNDSS): A voluntary collaboration between the CDC and the Council of State and Territorial Epidemiologists (CSTE). States mandate that local clinicians, hospitals, and clinical laboratories report specific infectious diseases to local/state health departments. The state health departments then voluntarily transmit de-identified case data to the CDC for nationwide surveillance.
• Mandatory Reporters: Under state laws, healthcare providers (physicians, clinical pharmacists, advanced practice nurses), infection preventionists, and clinical laboratory directors are legally mandated reporters. Failure to report carries civil penalties, fines, or professional licensure sanctions.

Stratified Reporting Timelines and Urgent Notification

State reporting statutes classify notifiable conditions into rigid temporal urgency tiers:

1. Immediate Reporting (< 24 Hours / Urgent Telephone Alert):
   • Pathogens of extreme transmissibility, bioterrorism potential, or immediate public health threat requiring instant contact tracing, isolation, or mass post-exposure prophylaxis (PEP).
   • Examples: Measles (rubeola), Invasive Meningococcal Disease (Neisseria meningitidis), Inhalation/Cutaneous Anthrax (Bacillus anthracis), Botulism (Clostridium botulinum), Rabies (human or animal bite), Smallpox, Viral Hemorrhagic Fevers (Ebola, Marburg), Diphtheria (Corynebacterium diphtheriae), Poliomyelitis, Novel Influenza A strains with pandemic potential.
2. Prompt / Routine Reporting (Within 1 to 3–5 Business Days):
   • Endemic or systemic communicable diseases requiring epidemiologic investigation, partner notification, or chronic disease management.
   • Examples: Active Tuberculosis (Mycobacterium tuberculosis), Syphilis (Treponema pallidum), Gonorrhea (Neisseria gonorrhoeae), Chlamydia (Chlamydia trachomatis), HIV infection (new diagnoses and viral load/CD4 laboratory reporting), Acute and Chronic Hepatitis A, B, and C, Lyme disease, Salmonellosis, Shigellosis, Shiga toxin-producing E. coli (STEC), Legionellosis, Babesiosis, Malaria.

Contact Tracing and Expedited Partner Therapy (EPT)

• Contact Tracing: Public health disease intervention specialists (DIS) interview index patients to identify exposed contacts, initiate diagnostic testing, provide counseling, and administer post-exposure prophylaxis (e.g., rifampin, ceftriaxone, or ciprofloxacin for close contacts of meningococcal disease; MMR vaccine within 72 hours or immune globulin within 6 days for measles contacts).
• Expedited Partner Therapy (EPT): Clinical practice where clinicians provide prescriptions or medications directly to the index patient to take to their heterosexual sexual partners without the healthcare provider first examining the partner. Supported by the CDC and legally permissible in most U.S. states for chlamydia and gonorrhea to prevent reinfection.

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ACIP Adult Immunization Recommendations: Core Vaccines

The CDC Advisory Committee on Immunization Practices (ACIP) issues annually updated adult immunization schedules. Recommendations are stratified by age cohorts and underlying medical risk conditions.

                    ACIP ADULT PNEUMOCOCCAL ALGORITHM (≥ 65 YEARS
                       OR 19–64 WITH SPECIFIED RISK CONDITIONS)

                        ┌──────────────────────────────┐
                        │   Pneumococcal Vaccine-Naive  │
                        │     (or Status Unknown)      │
                        └──────────────┬───────────────┘
                                       │
         ┌─────────────────────────────┼─────────────────────────────┐
         │                             │                             │
         ▼                             ▼                             ▼
┌─────────────────┐           ┌─────────────────┐           ┌─────────────────┐
│      PCV20      │           │      PCV21      │           │      PCV15      │
│ (Prevnar 20)    │           │   (Capvaxive)   │           │  (Vaxneuvance)  │
│   Single Dose   │           │   Single Dose   │           │   Single Dose   │
└─────────────────┘           └─────────────────┘           └────────┬────────┘
                                                                     │
                                                                     │ Followed by
                                                                     ▼
                                                            ┌─────────────────┐
                                                            │     PPSV23      │
                                                            │ (Pneumovax 23)  │
                                                            │ ≥ 8w or ≥ 1y*   │
                                                            └─────────────────┘
* Spacing for PPSV23 after PCV15: ≥ 8 weeks for immunocompromised, asplenia, CSF leak, cochlear implant;
  ≥ 1 year for immunocompetent adults ≥ 50 years or 19–49 with chronic medical conditions.

1. Pneumococcal Immunization Strategies

• Pneumococcal Vaccine Formulations:
  • Conjugate Vaccines (PCV15, PCV20, PCV21): Capsular polysaccharides chemically conjugated to a non-toxic diphtheria carrier protein ($CRM_{197}$). This conjugation recruits CD4+ T helper cells, inducing a T-cell dependent immune response. This produces high-avidity IgG, mucosal secretory IgA, and long-lived memory B cells. PCV21 (Capvaxive) is specifically engineered for adult invasive pneumococcal disease (IPD), covering 21 serotypes responsible for ~84% of adult IPD.
  • Polysaccharide Vaccine (PPSV23): 23 unconjugated purified capsular polysaccharides. Induces a T-cell independent B-cell response, stimulating mature B cells to produce IgM without memory B-cell generation. Repeated doses can induce immune tolerance or "hyporesponsiveness."
• Current ACIP Clinical Practice Algorithms:
  • Cohorts Eligible for Pneumococcal Vaccination:
    1. All adults aged ≥ 50 years. ACIP lowered the routine age-based threshold from 65 to 50 years in October 2024 (MMWR 2025;74:1), so a PCV-naive 52-year-old with no comorbidity is now due for a dose.
    2. Adults aged 19 to 49 years with underlying medical conditions:
       • Immunocompromising conditions: HIV infection, hematologic/solid organ malignancies, multiple myeloma, solid organ transplant, anatomical or functional asplenia, chronic renal failure, nephrotic syndrome, immunosuppressive drugs (corticosteroids, biologics, chemotherapy).
       • Chronic medical conditions: Chronic heart failure, cardiomyopathy, chronic obstructive pulmonary disease (COPD), asthma, chronic liver disease, cirrhosis, diabetes mellitus, alcoholism, cigarette smoking.
       • Anatomical barrier leaks: Cerebrospinal fluid (CSF) leaks, cochlear implants.
  • Recommended Regimens for Vaccine-Naive Adults:
    • Option A: Single dose of PCV20 alone (no subsequent PPSV23 needed).
    • Option B: Single dose of PCV21 alone (no subsequent PPSV23 needed).
    • Option C: Single dose of PCV15, followed by a dose of PPSV23.
  • Spacing Rules for Option C (PCV15 followed by PPSV23):
    • Immunocompetent adults ≥ 50 years OR adults 19–49 with chronic medical conditions: Minimum interval between PCV15 and PPSV23 is ≥ 1 year.
    • Adults with immunocompromising conditions, asplenia, CSF leak, or cochlear implants: Minimum interval between PCV15 and PPSV23 is ≥ 8 weeks (to achieve rapid antibody protection).
  • Prior PPSV23 Only History: Adults who previously received PPSV23 alone should receive a single dose of PCV20 or PCV21 at least 1 year after their last PPSV23 dose.

2. Respiratory Viral Vaccines (Influenza, COVID-19, RSV)

• Annual Influenza Vaccination:
  • Indicated annually for all individuals aged ≥ 6 months.
  • Preferential Recommendations for Adults Aged ≥ 65 Years: ACIP preferentially recommends one of three higher-immunogenicity formulations to overcome immunosenescence:
    1. High-Dose Inactivated Influenza Vaccine (HD-IIV4, Fluzone High-Dose): Contains 4× the antigen content (60 mcg hemagglutinin per strain vs. 15 mcg standard).
    2. Recombinant Influenza Vaccine (RIV4, Flublok): Contains 3× hemagglutinin antigen, manufactured using recombinant baculovirus expression without egg proteins.
    3. Adjuvanted Inactivated Influenza Vaccine (aIIV4, Fluad): Formulated with the oil-in-water squalene emulsion adjuvant MF59 to boost immune response.
  • Egg Allergy Guidance: The CDC/ACIP explicitly states that individuals with egg allergy of any severity may receive any licensed, age-appropriate influenza vaccine without special waiting periods or allergy consultation.
• COVID-19 Vaccination:
  • In September 2025 ACIP moved COVID-19 vaccination to individual-based decision-making (listed as shared clinical decision-making on the CDC schedule) for everyone aged ≥ 6 months, rather than a blanket annual recommendation for all adults.
  • The risk–benefit balance is most favorable for adults at increased risk of severe COVID-19 (age ≥ 65 years, immunocompromise, chronic cardiopulmonary, renal, hepatic, or metabolic disease) and least favorable for healthy younger adults; a documented prescriber or pharmacist discussion supports coverage.
  • Updated monovalent formulations target currently circulating variants, and moderately or severely immunocompromised adults may receive additional doses.
• Respiratory Syncytial Virus (RSV) Vaccines:
  • Vaccine Types: Recombinant protein subunit vaccines (Arexvy [adjuvanted with AS01E], Abrysvo [unadjuvanted bivalent RSVpreF]) and mRNA-1345 (mResvia).
  • Adult Recommendations: A single lifetime dose is recommended for all adults aged ≥ 75 years, and for adults aged 50 to 74 years at increased risk of severe RSV disease (chronic heart failure, COPD, asthma, end-stage renal disease, severe diabetes, obesity, nursing home residency). ACIP expanded the risk-based group from 60–74 down to 50–74 years in 2025.
  • Maternal RSV Immunization: Abrysvo is administered to pregnant individuals at 32 0/7 through 36 6/7 weeks of gestation between September and January in most of the continental U.S. to stimulate maternal antibodies that cross the placenta, providing passive protection to infants against severe RSV lower respiratory tract disease from birth through 6 months.

3. Herpes Zoster (Shingrix)

• Recombinant Zoster Vaccine (RZV, Shingrix): Non-live recombinant subunit vaccine combining varicella-zoster virus glycoprotein E with the AS01B adjuvant system. (The older live-attenuated Zostavax is discontinued and obsolete).
• Indications:
  • All immunocompetent adults aged ≥ 50 years.
  • Adults aged ≥ 19 years who are or will be immunocompromised.
• Schedule: 2-dose intramuscular series administered at 0 and 2 to 6 months (interval may be shortened to 0 and 1 to 2 months for immunocompromised individuals requiring rapid protective antibody induction).
• Special Instructions: Must be administered regardless of a prior history of clinical shingles and regardless of prior receipt of live Zostavax.

4. Tetanus, Diphtheria, Pertussis (Tdap / Td)

• General Adult Schedule: Adults who have never received Tdap should receive a single dose of Tdap, followed by a Td or Tdap booster every 10 years.
• Pregnancy Mandate: A dose of Tdap must be administered during every pregnancy, optimally between 27 and 36 weeks of gestation, regardless of the patient's previous tetanus or Tdap vaccination history. Administration during the early third trimester maximizes the transplacental transfer of maternal pertussis antibodies to the fetus, protecting the newborn during the high-mortality window prior to the 2-month childhood primary series.

5. Hepatitis B Vaccination

• Universal Recommendation: All adults aged 19 through 59 years should receive universal hepatitis B vaccination.
• Adults Aged ≥ 60 Years: Recommended for adults ≥ 60 with risk factors (diabetes mellitus, chronic liver disease, end-stage renal disease on hemodialysis, HIV infection, HCV infection, injection drug use, men who have sex with men, healthcare workers, incarcerated individuals) or any adult ≥ 60 who requests protection.
• Formulations: 2-dose series (Heplisav-B [CpG 1018 adjuvant] given at 0 and 1 month) or 3-dose series (Engerix-B, Recombivax HB at 0, 1, 6 months; or PreHevbrio 3-antigen at 0, 1, 6 months).

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Specialized High-Risk Immunization: Asplenia and Complement Deficiency

Patients with anatomical asplenia (splenectomy), functional asplenia (sickle cell disease), or persistent terminal complement pathway deficiencies (C5–C9, properdin, factor D/H), as well as patients treated with complement inhibitors (eculizumab, ravulizumab), are at catastrophic risk for Overwhelming Post-Splenectomy Infection (OPSI) and fulminant meningococcemia.

                 ENCAPSULATED ORGANISM DEFENSE IN ASPLENIA

 Loss of Splenic Macrophage Phagocytosis + Depleted Properdin / Tuftsin
                                     │
                                     ▼
               Catastrophic Vulnerability to Encapsulated Bacteria
   (Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae)
                                     │
                                     ▼
                  MANDATORY 4-VACCINE SPECIALIZED REGIMEN
   ┌───────────────────────┬───────────────────────┬───────────────────────┐
   │      Pneumococcal     │      MenACWY          │         MenB          │
   │  PCV20 or PCV21 alone │  2-dose primary (8w)  │  2-dose (Bexsero) OR  │
   │  OR PCV15 + PPSV23    │  Booster every 5 yrs  │  3-dose (Trumenba)    │
   └───────────────────────┴───────────────────────┴───────────────────────┘
   Plus: Haemophilus influenzae type b (Hib) — 1 dose if not previously received

Comprehensive Asplenia / Complement Deficiency Vaccination Protocol

1. Meningococcal Conjugate (MenACWY - Menveo or MenQuadfi):
   • Primary Series: 2 doses administered at least 8 weeks apart.
   • Booster Dosing: Re-vaccinate with MenACWY every 5 years throughout life as long as the anatomical or functional deficiency persists.
2. Meningococcal Serogroup B (MenB):
   • Primary Series: Either Bexsero (2 doses at 0 and 1 month) OR Trumenba (3 doses at 0, 1 to 2, and 6 months). (Brands are not interchangeable).
   • Booster Dosing: Administer a MenB booster dose 1 year following completion of the primary series, followed by booster doses every 2 to 3 years thereafter.
3. Pneumococcal Vaccination:
   • Single dose of PCV20 or PCV21 alone (or PCV15 followed ≥ 8 weeks later by PPSV23).
4. Haemophilus influenzae type b (Hib):
   • Single dose of Hib conjugate vaccine if not previously administered in adulthood.
5. Elective Splenectomy Timing:
   • For planned splenectomy, vaccines must be administered at least 14 days prior to surgery. If administered post-operatively, wait at least 14 days after surgery to ensure adequate immunogenicity.