16.3 Adult Immunization & Vaccines in Special Populations

Mastery of adult immunization schedules, vaccine indications in vulnerable patient populations, biostatistical calculations, diagnostic test performance, and epidemiological study design is essential for clinical practice and consistently tested on the ABIM Internal Medicine Board Examination.

1. CDC / ACIP Adult Immunization Schedule (2024–2026 Standards)

A. Pneumococcal Vaccination

• Target Populations:
  1. All adults aged >= 65 years (universal recommendation).
  2. Adults aged 19 to 64 years with Chronic Medical Conditions: Diabetes mellitus, chronic heart failure/cardiomyopathy, chronic lung disease (COPD, asthma, interstitial lung disease), chronic liver disease (cirrhosis, hepatitis), alcohol use disorder, current cigarette smoking, cerebrospinal fluid (CSF) leaks, or cochlear implants.
  3. Adults aged 19 to 64 years with Immunocompromising Conditions: Functional or anatomic asplenia (sickle cell disease, splenectomy), HIV infection (any CD4 count), chronic renal failure / end-stage renal disease (ESRD) on hemodialysis, nephrotic syndrome, leukemia, lymphoma, Hodgkin disease, generalized malignancy, solid organ transplant, multiple myeloma, or iatrogenic immunosuppression (radiation, systemic chemotherapy, prolonged high-dose corticosteroids >=20 mg prednisone daily for >=14 days, or biologic immunosuppressants).
• Recommended Pneumococcal Regimens (Pneumococcal Conjugate Vaccine [PCV] vs. Polysaccharide Vaccine [PPSV]):
  • Option 1 (Single-Dose Conjugate Alone - Preferred Modern Regimen):
    • Administer 1 single dose of PCV20 (Prevnar 20) OR PCV21 (Capvaxive) alone. No subsequent PPSV23 booster is needed.
  • Option 2 (Sequential Conjugate + Polysaccharide Regimen):
    • Administer 1 dose of PCV15 (Vaxneuvance) followed by 1 dose of PPSV23 (Pneumovax 23).
    • Interval between PCV15 and PPSV23: >= 1 year for immunocompetent individuals; shortened to >= 8 weeks for immunocompromised individuals, patients with CSF leaks, or cochlear implants.

B. Herpes Zoster (Shingles) Vaccination

• Recombinant Zoster Vaccine (RZV / Shingrix):
  • Dosing Schedule: 2-dose series administered intramuscularly at 0 and 2 to 6 months.
  • Target Population:
    • All immunocompetent adults aged >= 50 years, regardless of whether they have a prior history of shingles, herpes zoster ophthalmicus, or previous receipt of the older live zoster vaccine (Zostavax [ZVL]).
    • Immunocompromised adults aged >= 19 years (give 2nd dose at 1 to 2 months).
  • Key Note: Live zoster vaccine (Zostavax) has been discontinued. Shingrix is a non-live recombinant subunit vaccine and is safe in immunocompromised hosts.

C. Respiratory Syncytial Virus (RSV) Vaccination

• ACIP Recommendations (Arexvy [GSK] or Abrysvo [Pfizer]):
  • All adults aged >= 75 years: Administer a single dose of RSV vaccine.
  • Adults aged 60 to 74 years: Administer a single dose of RSV vaccine if at increased risk of severe RSV disease:
    • Chronic cardiovascular disease (heart failure, coronary artery disease),
    • Chronic pulmonary disease (COPD, asthma, pulmonary fibrosis),
    • Chronic kidney disease (stage 3–5 or ESRD),
    • Chronic liver disease,
    • Diabetes mellitus with end-organ damage,
    • Severe obesity (BMI >=40 kg/m2),
    • Residents of nursing homes and long-term care facilities.

D. COVID-19 & Influenza Vaccination

• COVID-19 Vaccine: Administer an annual updated COVID-19 vaccine formulation to all individuals aged >= 6 months.
• Influenza Vaccine: Administer an annual influenza vaccine to all individuals aged >= 6 months.
  • Adults aged >= 65 years: Preferential administration of higher-dose or adjuvanted influenza vaccines to overcome immunosenescence:
    1. High-Dose Inactivated Influenza Vaccine (Fluzone High-Dose Quadrivalent),
    2. Recombinant Influenza Vaccine (Flublok Quadrivalent), OR
    3. Adjuvanted Inactivated Influenza Vaccine (Fluad Quadrivalent).
  • Egg Allergy: Current guidelines state that any age-appropriate influenza vaccine (inactivated or recombinant) can be administered to patients with egg allergy of any severity without special precautions.

E. Tetanus, Diphtheria, Pertussis (Td / Tdap) & Wound Management

• Routine Dosing: Administer 1 dose of Tdap to all adults who have not received it previously, followed by a Td or Tdap booster every 10 years.
• Pregnancy: Administer 1 dose of Tdap during EACH pregnancy, ideally between 27 and 36 weeks gestation, to maximize transplacental transfer of maternal pertussis antibodies to the neonate, regardless of the interval since prior Tdap doses.
• Tetanus Prophylaxis in Wound Management:

F. Hepatitis B & Human Papillomavirus (HPV) Vaccination

• Hepatitis B: Universal vaccination for all adults aged 19 to 59 years (2-dose series with Heplisav-B at 0 and 1 month, or 3-dose series with Engerix-B/Recombivax HB at 0, 1, and 6 months). For adults aged >=60 years, vaccinate if risk factors are present (diabetes, hemodialysis, chronic liver disease, HIV, HCV, injection drug use, MSM, incarcerated) or if the patient requests protection.
• Human Papillomavirus (HPV): 9-valent HPV vaccine (Gardasil-9) recommended routinely through age 26 years. In adults aged 27 to 45 years, use clinical shared decision-making (greatest benefit in individuals with new sexual partners who were not previously infected/vaccinated).

2. Vaccines in Special Populations

A. Immunocompromised Host Contraindications

• Absolute Rule: LIVE ATTENUATED VACCINES ARE STRICTLY CONTRAINDICATED in severely immunocompromised patients, solid organ transplant recipients, active hematologic malignancy, severe primary immunodeficiencies, HIV with CD4 <200 cells/mcL, or patients taking high-dose systemic immunosuppression (>=20 mg/day prednisone equivalent for >=14 days, anti-TNF-alpha biologics, antimetabolites, calcineurin inhibitors).
• Contraindicated Live Vaccines:
  • Measles, Mumps, Rubella (MMR),
  • Varicella vaccine (Varivax),
  • Live Attenuated Influenza Vaccine (LAIV - Flumist nasal spray),
  • Yellow Fever vaccine,
  • Oral Typhoid vaccine (Ty21a).

B. Asplenia & Functional Asplenia Immunization Protocol

Patients with anatomic asplenia (post-splenectomy) or functional asplenia (sickle cell disease) are at catastrophic risk for Overwhelming Post-Splenectomy Infection (OPSI) caused by encapsulated bacteria. They require a dedicated vaccination bundle:

1. Pneumococcal Series: Single-dose PCV20 (or PCV15 followed by PPSV23 >=8 weeks later).
2. Meningococcal Conjugate (MenACWY - Menveo / MenQuadfi): 2-dose primary series administered 8 weeks apart, followed by a booster dose every 5 years.
3. Serogroup B Meningococcal (MenB - Bexsero / Trumenba): 2-dose (Bexsero at 0, 1 month) or 3-dose (Trumenba at 0, 1–2, 6 months) series, with booster 1 year later and q2–3y.
4. Haemophilus influenzae type b (Hib): 1 dose.
5. Annual Inactivated Influenza Vaccine.

• Timing of Administration: In elective splenectomy, administer all vaccines >=14 days prior to surgery. In emergency splenectomy, administer vaccines >=14 days postoperatively (or upon hospital discharge) to achieve optimal antibody titers.