2.3 Viral Hepatitis (Hep A & B), Polio, and Enteric/GI Infections
Key Takeaways
- Hepatitis A Virus (HAV, Picornaviridae) spreads primarily via the fecal-oral route through contaminated food/water or close personal contact; inactivated HAV vaccines (Havrix, Vaqta) provide long-lasting immunity via a 2-dose series.
- Hepatitis B Virus (HBV, Hepadnaviridae) is a bloodborne and sexually transmitted pathogen that establishes chronic hepatitis in up to 90% of infected infants and 5% of adults, progressing to cirrhosis and hepatocellular carcinoma (HCC).
- Current CDC guidance uses individual/shared decision-making for Hepatitis B vaccination of infants born to HBsAg-negative mothers; infants born to mothers who are HBsAg-positive or whose status is unknown still require prompt birth-dose prophylaxis. Adult HepB vaccination remains universal at ages 19 through 59, with risk-based or request-based vaccination at age 60 and older. PreHevbrio has been withdrawn and remaining vials should not be used.
- Poliovirus causes irreversible asymmetric flaccid paralysis by destroying anterior horn motor neurons; the United States exclusively administers Inactivated Poliovirus Vaccine (IPV, Salk) to eliminate the risk of Vaccine-Associated Paralytic Poliomyelitis (VAPP) inherent to live Oral Poliovirus Vaccine (OPV, Sabin).
- Rotavirus (Reoviridae) causes severe dehydrating diarrhea and metabolic acidosis in infants. The January 2026 childhood schedule places rotavirus vaccination under shared clinical decision-making; when selected, Rotarix (2 doses) or RotaTeq (3 doses) must be initiated before 15 weeks of age and completed before 8 months, with screening for intussusception and SCID.
2.3 Viral Hepatitis (Hep A & B), Polio, and Enteric/GI Infections
Gastrointestinal and hepatic viral pathogens impose severe systemic burdens ranging from acute fulminant hepatic necrosis and dehydrating infantile diarrhea to chronic oncogenesis and permanent paralytic myelitis. Understanding transmission routes, serological interpretations, and product-specific administration protocols is a core competency for pharmacy technicians.
1. Hepatitis A Virus (HAV)
Hepatitis A is an acute, self-limiting liver infection caused by the Hepatitis A Virus (HAV), a small, non-enveloped, positive-sense, single-stranded RNA virus belonging to the family Picornaviridae (genus Hepatovirus).
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| HEPATITIS A TRANSMISSION & COURSE |
| |
| [ FECAL-ORAL TRANSMISSION ] |
| - Ingestion of food or water contaminated with fecal matter (shellfish) |
| - Close personal contact (household contacts, sexual partners) |
| - Illicit drug use (injection and non-injection) / Persons experiencing |
| homelessness / International travelers to endemic regions |
| │ |
| ▼ |
| [ INCUBATION PERIOD: 15–50 DAYS (AVERAGE 28 DAYS) ] |
| - Viral replication in hepatocytes; excreted in bile and feces |
| - Maximum infectivity occurs 2 WEEKS PRIOR to onset of jaundice |
| │ |
| ▼ |
| [ CLINICAL MANIFESTATIONS ] |
| - Children < 6 years: Usually ASYMPTOMATIC (> 70% have no jaundice) |
| - Adults: > 70% SYMPTOMATIC (Abrupt fever, malaise, anorexia, nausea, |
| RUQ abdominal pain, dark urine [bilirubinuria], clay-colored acholic |
| stools, and marked scleral/cutaneous icterus) |
| - Marked serum aminotransferase elevation (ALT and AST > 1,000 U/L) |
| │ |
| ▼ |
| [ CLINICAL OUTCOME ] |
| - Complete recovery with lifelong protective immunity |
| - NO CHRONIC CARRIER STATE OR CHRONIC INFECTION |
| - Acute fulminant hepatic failure occurs in < 1% (elevated risk in |
| underlying chronic liver disease: Hep B, Hep C, cirrhosis) |
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Hepatitis A Vaccine Products and Current Indications
- Inactivated Whole-Virus Vaccines: Havrix and Vaqta (inactivated with formalin and adsorbed to aluminum hydroxide adjuvant).
- Dosing Schedule: 2-dose series administered intramuscularly with a minimum interval of 6 months (0 and 6–12 months for Havrix; 0 and 6–18 months for Vaqta).
- Current U.S. Categories: The January 2026 childhood schedule places HepA vaccination under shared clinical decision-making for otherwise healthy children while retaining recommendations for specified high-risk groups and populations. Indications include people experiencing homelessness, men who have sex with men, people with chronic liver disease, international travelers, and others identified in current CDC guidance; follow the current schedule and notes.
2. Hepatitis B Virus (HBV)
Hepatitis B is a life-threatening hepatic infection caused by the Hepatitis B Virus (HBV), an enveloped, partially double-stranded circular DNA virus of the family Hepadnaviridae. HBV replicates via an RNA intermediate using reverse transcriptase.
Virion Structure and Key Antigens
- Hepatitis B Surface Antigen (HBsAg): Envelope glycoprotein displayed on the virion surface; presence indicates active HBV infection (acute or chronic). It is the target antigen used in all Hepatitis B vaccines.
- Hepatitis B Core Antigen (HBcAg): Nucleocapsid protein surrounding the viral DNA genome. Intracellular antigen; not detected free in serum, but triggers production of anti-HBc antibodies.
- Hepatitis B e-Antigen (HBeAg): Secretory protein processed from the precore protein; serves as a serum biomarker for high viral replication, active viral turnover, and high transmission risk.
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| HEPATITIS B SEROLOGY INTERPRETATION |
| |
| SEROLOGICAL MARKER SUSCEPTIBLE NATURAL IMMUNITY VACCINE IMMUNITY |
| ────────────────── ─────────── ──────────────── ──────────────── |
| HBsAg (Surface Ag) (-) (-) (-) |
| Anti-HBs / HBsAb (Surface) (-) (+) (+) |
| Anti-HBc Total (Core Ab) (-) (+) (-) |
| Anti-HBc IgM (Acute Core) (-) (-) (-) |
| |
| *Key Rule: Anti-HBc is positive ONLY after natural infection. |
| Vaccinated individuals develop antibodies ONLY to HBsAg (Anti-HBs (+)). |
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Pathophysiology, Chronicity, and Oncogenesis
Transmission occurs percutaneously or mucosally through contact with infectious blood, semen, and vaginal secretions (sexual contact, sharing needles/syringes, healthcare occupational exposure, and perinatal vertical transmission from mother to newborn).
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| AGE-DEPENDENT RISK OF CHRONIC HEPATITIS B |
| |
| INFANTS (Perinatal Transmission) ────────► 90% PROGRESS TO CHRONIC HBV |
| CHILDREN (1 to 5 Years) ─────────────────► 25%–50% PROGRESS TO CHRONIC HBV|
| ADULTS & ADOLESCENTS ────────────────────► < 5% PROGRESS TO CHRONIC HBV |
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Chronic HBV Sequelae: Persistent infection causes continuous immune-mediated hepatic destruction, leading to chronic hepatitis, progressive hepatic fibrosis, macronodular cirrhosis, end-stage liver disease with portal hypertension, and Hepatocellular Carcinoma (HCC). HBV DNA can integrate directly into host hepatocyte genomes, driving insertional mutagenesis and direct oncogenesis even in the absence of established cirrhosis.
Modern Hepatitis B Vaccine Formulations
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| HEPATITIS B VACCINE PRODUCTS & SCHEDULES |
| |
| 1. RECOMBINANT SINGLE-ANTIGEN (Yeast-Derived HBsAg) |
| - Products: Engerix-B, Recombivax HB. |
| - Schedule: Standard 3-dose series at 0, 1, and 6 months (IM). |
| - Pediatric birth dose: give HepB vaccine plus HBIG within 12 hours when the mother is HBsAg-positive; when maternal status is unknown, follow the weight- and status-specific urgent prophylaxis algorithm. For an HBsAg-negative mother, current CDC guidance uses individual/shared decision-making; if deferred, CDC suggests starting no earlier than age 2 months. |
| |
| 2. 2-DOSE ADJUVANTED RECOMBINANT (CpG 1018 Adjuvant) |
| - Product: Heplisav-B (Dynavax). Formulated with yeast-derived HBsAg + CpG 1018 adjuvant |
| (a synthetic Toll-like Receptor 9 [TLR9] agonist). |
| - Schedule: 2 doses administered 1 month apart (0, 1 month) (IM). |
| - Approved ONLY for adults aged ≥ 18 years. Produces significantly higher and faster |
| seroprotection rates (≥ 95%) in historically hyporesponsive cohorts (diabetes, obesity, |
| chronic kidney disease, smokers, older adults). |
| |
| 3. WITHDRAWN PRODUCT (DO NOT USE) |
| - PreHevbrio was voluntarily withdrawn from the U.S. market; FDA says remaining vials |
| should not be used. The withdrawal was related to manufacturer operations, not a safety signal. |
| |
| 4. COMBINATION HEPATITIS A & HEPATITIS B |
| - Product: Twinrix (Inactivated HAV + Recombinant HBsAg). |
| - Schedule: Standard 3 doses at 0, 1, and 6 months; or Accelerated 4-dose schedule: |
| 0, 7, and 21–30 days, followed by a booster at 12 months. Approved for ages ≥ 18 years. |
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[!IMPORTANT] Adult Hepatitis B Recommendation: CDC recommends Hepatitis B vaccination for all adults aged 19 through 59 years, regardless of reported risk factors. Adults aged 60 years and older with risk factors—or any adult aged 60 or older seeking protection—should also be vaccinated. This adult recommendation is distinct from the current individual/shared decision framework for many infants born to HBsAg-negative mothers.
3. Poliomyelitis (Poliovirus)
Poliomyelitis is an acute, crippling communicable disease caused by Poliovirus, an enterovirus belonging to the family Picornaviridae. Poliovirus is a non-enveloped positive-sense single-stranded RNA virus existing in three distinct serotypes: Type 1, Type 2, and Type 3.
Pathogenesis and Neurotropism
- Transmission: Primary transmission occurs via the fecal-oral route (ingestion of contaminated water/food) and secondarily via oral-oral pharyngeal secretions.
- Infection Course: Virus enters the oropharynx, multiplies in the tonsillar lymphoid tissue and gastrointestinal Peyer's patches, and sheds into the stool. It disseminates through cervical and mesenteric lymph nodes into the bloodstream (viremia).
- Central Nervous System Invasion: In approximately 0.5% to 1% of infections, poliovirus crosses the blood-brain barrier and selectively infects and lyses anterior horn motor neurons of the spinal cord and motor nuclei of the brainstem.
- Clinical Manifestations: Destruction of lower motor neurons causes Acute Flaccid Paralysis (AFP). The paralysis is typically asymmetric, affects proximal muscle groups more severely than distal muscles, preserves sensory function entirely, and results in flaccidity with loss of deep tendon reflexes. Bulbar polio involves cranial nerve motor nuclei, leading to respiratory failure, dysphagia, and circulatory collapse.
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| INACTIVATED (IPV - SALK) VS. ORAL (OPV - SABIN) POLIO VACCINES |
| |
| FEATURE IPV (SALK) - INACTIVATED OPV (SABIN) - LIVE ATTENUATED |
| ────────────────────── ─────────────────────────────── ───────────────────────────── |
| Formulation Formalin-inactivated (Types 1,2,3) Live attenuated viral strains |
| Administration Route Intramuscular or Subcutaneous Oral drops (GI mucosal exposure) |
| Immune Response High serum IgG (prevents viremia Secretory mucosal IgA + serum IgG; |
| and central motor neuron invasion) induces contact herd immunity |
| Mucosal Shedding Allows transient intestinal shed Blocks wild virus gut transmission |
| VAPP Risk ZERO RISK OF VAPP Causes VAPP (~1 in 2.4 million) |
| Circulating VDPV CANNOT generate cVDPV mutations Can revert to neurovirulent cVDPV |
| U.S. Current Usage 100% EXCLUSIVE U.S. SCHEDULE DISCONTINUED IN U.S. SINCE 2000 |
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[!NOTE] Why the U.S. Uses IPV Exclusively: In 2000, the United States eliminated OPV from its routine childhood immunization schedule, adopting an all-IPV schedule (4 doses at 2, 4, 6–18 months, and 4–6 years). Because wild poliovirus had been eliminated from the Western Hemisphere, the small residual risk of Vaccine-Associated Paralytic Poliomyelitis (VAPP) from OPV reversion became unacceptable.
4. Enteric Viral Infections: Rotavirus
Rotavirus is a non-enveloped, double-stranded RNA virus belonging to the family Reoviridae, characterized by a distinct wheel-like (wheel = rota) capsid architecture under electron microscopy. It is the primary worldwide cause of severe dehydrating gastroenteritis in infants and young children.
Pathophysiology
- Transmitted via the fecal-oral route through direct contact, fomites, and contaminated fluids.
- Inoculum infects and lyses mature, non-dividing absorptive enterocytes on the villi of the small intestine, sparing crypt cells. This blunts intestinal villi, producing severe osmotic malabsorption.
- Rotavirus non-structural protein 4 (NSP4) acts as a viral enterotoxin, stimulating calcium release within enterocytes, inducing chloride secretion, and triggering autonomic nervous system reflexes that accelerate gut motility.
- Results in sudden onset of watery, non-bloody, copious diarrhea, projectile vomiting, fever, rapid severe dehydration, hypokalemia, and metabolic acidosis.
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| ROTAVIRUS VACCINES & CRITICAL TIMING RULES |
| |
| 1. ROTARIX (RV1 - GlaxoSmithKline) |
| - Composition: Live attenuated human monovalent strain (G1P[8]). |
| - Dosing Schedule: 2-DOSE ORAL SERIES at 2 months and 4 months of age. |
| |
| 2. ROTATEQ (RV5 - Merck) |
| - Composition: Live human-bovine reassortant pentavalent strains (G1, G2, G3, G4, P1A[8]). |
| - Dosing Schedule: 3-DOSE ORAL SERIES at 2 months, 4 months, and 6 months of age. |
| |
| CRITICAL AGE WINDOWS (STRICT CDC/ACIP PARAMETERS): |
| • Minimum Age for Dose 1: 6 weeks |
| • MAXIMUM AGE FOR DOSE 1: 14 WEEKS 6 DAYS (Do NOT initiate series if age ≥ 15 weeks 0 days) |
| • MAXIMUM AGE FOR FINAL DOSE: 8 MONTHS 0 DAYS (Do NOT administer any dose at or after 8 months) |
| • Minimum Interval Between Doses: 4 weeks |
| • Administration Route: STRICTLY ORAL (DO NOT INJECT) |
| |
| CONTRAINDICATIONS & SAFETY SCREENING: |
| • Severe Combined Immunodeficiency (SCID) |
| • Documented history of INTUSSUSCEPTION (telescoping of bowel segment causing bowel ischemia) |
| • Packaging-related allergy requires a current insert check; the current FDA-approved Rotarix oral dosing applicator is not made with natural rubber latex |
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A 42-year-old male with type 2 diabetes presents to the outpatient pharmacy clinic requesting a Hepatitis B immunization. Which of the following statements accurately reflects ACIP recommendations and product options for this adult?
Which of the following clinical considerations explains why the United States transitioned exclusively to an all-Inactivated Poliovirus Vaccine (IPV) schedule in 2000, completely discontinuing the live Oral Poliovirus Vaccine (OPV)?
A pharmacy technician is assisting in the preparation of pediatric vaccines. An infant is brought in for her first wellness visit at 16 weeks of age. The parent asks if the infant can begin the Rotavirus oral vaccine series today. How should the technician and pharmacist address this request?