Epidemiology and Prevention of Viral Hepatitis A to E: Hepatitis A Virus

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Epidemiology and Prevention of Viral Hepatitis A
to EHepatitis A Virus

• Division of Viral Hepatitis

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Hepatitis A Virus
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Geographic Distribution of HAV Infection
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Reported Cases of Hepatitis A, United States
1995 Vaccine Licensed
1996 ACIP recommendations
1999 ACIP recommendations
Source NNDSS, CDC
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States with Hepatitis A Rates gt 10/100,000 1987-97
Rate gt 20/100,000
Rate 10-20/100,000
Rate lt 10/100,000
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• Number of years that Reported Incidence of
• Hepatitis A Exceeded 10 Cases per 100,000,
• by County, 1987-1997

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Hepatitis A Incidence, United States
1987-97 average incidence
2002 incidence
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Top 10 States With the Highest Hepatitis A Rates
NOW 2001
THEN 1987-1997
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Basics of Hepatitis A

• RNA Picornavirus
• Single serotype worldwide
• Acute disease and asymptomatic infection
• No chronic infection
• Protective antibodies develop in response to
  infection - confers lifelong immunity

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Hepatitis A Clinical Features

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Acute Hepatitis A Case Definition For
Surveillance

• Clinical criteria of an acute illness with
• discrete onset of symptoms (e.g. fatigue,
  abdominal pain, loss of appetite, intermittent
  nausea, vomiting), and
• jaundice or elevated serum aminotransferase
  levels
• Laboratory criteria
• IgM antibody to hepatitis A virus (anti-HAV)
  positive
• Case Classification
• Confirmed. A case that meets the clinical case
  definition and is laboratory confirmed or a case
  that meets the clinical case definition and
  occurs in a person who has an epidemiologic link
  with a person who has laboratory-confirmed
  hepatitis A during the 15-50 days before the
  onset of symptoms.

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Events In Hepatitis A Virus Infection
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Concentration of Hepatitis A Virus in Various
Body Fluids
Feces
Serum
Body Fluids
Saliva
Urine
100
102
104
106
108
1010
Infectious Doses per mL
Source Viral Hepatitis and Liver Disease
19849-22 J Infect Dis 1989160887-890
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Hepatitis A Virus Transmission

• Fecal-oral
• Close personal contact(e.g., household contact,
  sex contact, child day care centers)
• Contaminated food, water(e.g., infected food
  handlers)
• Blood exposure (rare)(e.g., injecting drug use,
  transfusion)

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Global Patterns of Hepatitis A Virus Transmission
Disease Rate
Peak Age of Infection
Transmission Patterns
Endemicity
Low to high
Early childhood
High
Person to person
outbreaks uncommon
Late childhood/ young adults
High
Moderate
Person to person
food and waterborne
outbreaks
Low
Young adults
Low
Person to person
food and waterborne
outbreaks
Very low
Very low
Adults
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Risk Factors Associated with Reported Hepatitis
A, 1990-2000, United States
Source NNDSS/VHSP
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Prevention of Hepatitis A

• Vaccination (pre-exposure)
• Immune globulin
• Good hygiene
• Clean water systems avoidance of food
  contamination

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Hepatitis A Vaccination Strategy Epidemiologic
Considerations

• Many cases occur in community-wide outbreaks
• no risk factor identified for 40-50 of cases
• highest attack rates in 5-14 year olds
• children serve as reservoir of infection
• Groups at increased risk of infection
• travelers to developing countries
• men who have sex with men
• illegal drug users
• persons with chronic liver disease

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Hepatitis A Prevention Immune Globulin

• Pre-exposure
• travelers to intermediate and high HAV-endemic
  regions
• Post-exposure (within 14 days)
• Routine
• household and other intimate contacts
• Selected situations
• institutions (e.g., day care centers)
• common source exposure (e.g.,
• food prepared by infected food handler)

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ACIP Recommendations Hepatitis A Vaccine
Pre-exposure Vaccination

• Persons at increased risk for infection
• travelers to intermediate and high HAV-endemic
  countries
• MSM (Men who have sex with men)
• illegal drug users
• Persons who have clotting factor disorders
• persons with chronic liver disease
• Communities with historically high rates of
  hepatitis A -routine childhood vaccination

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Duration of Protection after Hepatitis A
Vaccination

• Persistence of antibody
• At least 5-8 years among adults and children
• Efficacy
• No cases in vaccinated children at 5-6 years of
  follow-up
• Mathematical models of antibody decline suggest
  protective antibody levels persist for at least
  20 years
• Other mechanisms, such as cellular memory, may
  contribute

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Hepatitis A VaccineImmunogenicity, Side Effects

• Immunogenicity in children, adolescents,
  adults
• 94-100 positive 1 month after dose 1
• 99-100 positive after dose 2
• Most common side effects
• Sore injection site (50), headache (15),
  malaise (7)
• No severe reactions known
• Safety in pregnancy unknown (risk likely is low)

Currently licensed for aged 1 year and older
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Use of Hepatitis A Vaccine for Infants

• Hepatitis A vaccine is licensed only for persons
  aged 1 year and older
• Safe and immunogenic for infants without maternal
  antibody
• Presence of passively-acquired maternal antibody
  blunts immune response
• all respond, but with lower final
• antibody concentrations
• Age by which maternal antibody disappears is
  unclear
• still present in some infants at one year
• probably gone in vast majority by 15 months

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ACIP Recommendations, 1999 Implementation

• Children Who Should be Routinely Vaccinated
• living in states, counties, and communities where
  the average hepatitis A rate was ? 20
  cases/100,000 during baseline period.
• Children Who Should be Considered for Routine
  Vaccination
• living in states, counties, and communities
  where the average hepatitis A rate was lt20 but ?
  10 cases/100,000 during the baseline period.

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ACIP Recommendations Hepatitis A Vaccine
Post-vaccination Testing

• Not recommended because of the high response rate
  among vaccinees (95 after dose one, 100 after
  two)
• No commercially available test to measure vaccine
  response

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Hepatitis A in the United States-2002

• National rate lowest yet recorded
• Continued monitoring needed to determine if low
  rates sustained and due to vaccination
• Evaluation of age-specific rates to assess impact
  of vaccination strategy
• Rates increasing in some states
• Occurring among adults in high risk groups (e.g.
  MSM, drug users)

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Long-term Hepatitis A Prevention Strategy

• Sustain ongoing vaccination
• Lower disease incidence
• Catch-up vaccination of children and adolescents
• Further reduce incidence
• Vaccination of high-risk adults
• Routine vaccination of all children nationwide