{
  "slug": "hepatitis-a-travel",
  "question": "What are the odds of contracting hepatitis A as an unvaccinated traveler to an endemic region?",
  "category": "health",
  "tags": [
    "travel"
  ],
  "no_reliable_estimate": false,
  "perceived": {
    "description": "Hepatitis A occupies an unusual slot in pre-travel anxiety: it sits on most travel-clinic recommendation lists for any trip outside the wealthy industrialized core, the vaccine is cheap and >97% effective after a single dose, and the CDC describes it as among the most common vaccine-preventable infections acquired during travel. The framing travelers receive is \"you almost certainly want this vaccine for any non-Western destination\", and unlike Japanese encephalitis or rabies the framing actually matches the underlying numbers. We haven't found a rigorous recent survey that isolates \"fear of hepatitis A\" from generic travel-disease worry, so the perceived side here is marked as editorial intuition rather than polled data. The working prior we observe in travel clinics is \"this is a real risk worth a $100 shot\" — and for an unvaccinated nonimmune adult on a two-week trip to a high or intermediate endemicity country, that prior is roughly calibrated.\n",
    "rough_estimate": "most unvaccinated travelers heading to an endemic country guess a per-trip risk on the order of 1-in-1,000 to 1-in-10,000",
    "kind": "intuition"
  },
  "native": {
    "display": "~8 cases per 100,000 nonimmune travelers per 2-week trip",
    "numerator": 8,
    "denominator": 100000,
    "unit": "per trip (2-week stay, high/intermediate endemicity)",
    "population": "Unvaccinated, nonimmune adult travelers from developed countries to high or intermediate hepatitis A endemicity regions"
  },
  "normalized": {
    "lifetime_us_adult": 0.00008,
    "display": "~1 in 12,000 per 2-week trip (unvaccinated, nonimmune, high/intermediate endemicity)",
    "log_value": -4.1,
    "assumptions": "Mütsch et al. (2006), the canonical traveler hepatitis A incidence study, reports 6.0–28.0 cases per 100,000 person-months abroad for travelers presumed to be nonimmune visiting countries of high or intermediate transmission risk. Converted to a typical 2-week trip (0.5 person-months), this is 3–14 cases per 100,000 travelers per trip; the point estimate of 8 × 10⁻⁵ (~1 in 12,000) is the midpoint of that range. The scope is activity_specific_lifetime: per traveler-trip, not per US-adult-lifetime. The CDC Yellow Book and the ACIP 2020 MMWR recommendation describe unvaccinated travelers to high or intermediate endemicity countries as facing a \"substantial risk\", and Mütsch's figures sit roughly 10–50× below older 1990s estimates (the Steffen-era ~3 per 1,000 per month) thanks to improved sanitation, water infrastructure, and tourist-zone hygiene across most destination countries. The uncertainty band reflects the population in the headline (nonimmune, 2-week, high/intermediate endemicity); cross-population variation (vaccinated travelers, long-rural stays, low-endemicity destinations, VFR families) is captured in regional_breakdown and personal_factor_multipliers.\n",
    "uncertainty": {
      "low": 0.00003,
      "high": 0.00014
    },
    "scope": "activity_specific_lifetime"
  },
  "sources": [
    {
      "url": "https://academic.oup.com/cid/article/42/4/490/382261",
      "title": "Hepatitis A Virus Infections in Travelers, 1988-2004",
      "publisher": "Clinical Infectious Diseases (Mütsch, Spicher, Gut, Steffen)",
      "source_type": "peer_reviewed",
      "statistic": "Incidence of hepatitis A in travelers to high or intermediate transmission risk countries: 3.0-11.0 per 100,000 person-months abroad for all travelers; 6.0-28.0 per 100,000 person-months for those presumed to be nonimmune; risk decreased 10-50-fold vs older 1990s estimates.",
      "excerpt": "\"The actual incidence of hepatitis A in travelers to countries of high or intermediate risk of transmission was 3.0–11.0 per 100,000 person-months abroad for all travelers and 6.0–28.0 per 100,000 for those presumed to be nonimmune. … The risk of hepatitis A virus infections has decreased by a factor of 10–50-fold over time, compared with findings from older studies. The risk, however, remains very considerable at many destinations, including frequently visited places, such as Mexico. Children of immigrants are a high-risk population.\"\n",
      "source_date": "2006-02-15",
      "source_accessed": "2026-05-24",
      "archive_url": "http://web.archive.org/web/20240430063641/https://academic.oup.com/cid/article/42/4/490/382261",
      "calculation_notes": "Mütsch et al. is the primary anchor for the headline figure. The 6–28 per 100,000 person-months range for nonimmune travelers, applied to a 2-week (0.5-month) trip, yields 3–14 per 100,000 trips. The point estimate of 8 × 10⁻⁵ (~1 in 12,000) is the midpoint. The uncertainty band ([3 × 10⁻⁵, 1.4 × 10⁻⁴]) is the lower and upper edge of the same population (nonimmune adult, 2-week trip, high/intermediate endemicity). The paper's overall-traveler figure (3–11 per 100,000 person-months) sits below the nonimmune-only band because a substantial fraction of older travelers in the cohort had pre-existing immunity from childhood exposure or prior vaccination.\n",
      "independence_note": "Mütsch et al. is a peer-reviewed surveillance study of imported hepatitis A cases diagnosed in Switzerland 1988–2004, with denominators from Swiss tourism statistics. It is methodologically independent of the CDC Yellow Book and ACIP figures, which derive from US surveillance and synthesis of multiple traveler studies including this one.\n"
    },
    {
      "url": "https://www.cdc.gov/yellow-book/hcp/travel-associated-infections-diseases/hepatitis-a.html",
      "title": "Hepatitis A — CDC Yellow Book",
      "publisher": "US Centers for Disease Control and Prevention",
      "source_type": "govt_report",
      "statistic": "Hepatitis A is among the most common vaccine-preventable infections acquired during travel. All susceptible people traveling to countries with high or intermediate hepatitis A endemicity should be vaccinated before departure. Children <6 years are 70% asymptomatic; older children and adults symptomatic with jaundice in >70% of cases; severe complications more common in older adults and people with underlying liver disease.",
      "excerpt": "\"Hepatitis A is among the most common vaccine-preventable infections acquired during travel. … All susceptible people traveling for any purpose, frequency, or duration to countries with high or intermediate hepatitis A endemicity should be vaccinated or receive IG before departure. … In children aged <6 years, most (70%) infections are asymptomatic; jaundice is uncommon in symptomatic young children. Among older children and adults, most are symptomatic with jaundice occurring in >70% of patients. … Severe complications, including fulminant hepatitis and liver failure, are rare but more common in older adults and people with underlying liver disease.\"\n",
      "source_date": "2024-05-01",
      "source_accessed": "2026-05-24",
      "archive_url": "http://web.archive.org/web/20260511095815/https://www.cdc.gov/yellow-book/hcp/travel-associated-infections-diseases/hepatitis-a.html",
      "calculation_notes": "CDC Yellow Book is the primary US clinical traveler-medicine reference and the source for the \"high or intermediate endemicity\" vocabulary used throughout the entry. Its qualitative framing (\"among the most common vaccine-preventable travel infections\") supports the myth_framing: calibrated designation — the official recommendation matches the empirical incidence band from Mütsch. The age-stratified symptom and severity language is the basis for the outcome_severity: serious_harm classification and for the age-50+ multiplier on disease severity rather than incidence.\n",
      "independence_note": "CDC Yellow Book is a CDC programmatic synthesis of traveler-medicine literature; it cites Mütsch among many other sources, so the two are partially dependent. Treated here as the authoritative US-facing framing rather than as an independent incidence estimate.\n"
    },
    {
      "url": "https://www.cdc.gov/mmwr/volumes/69/rr/rr6905a1.htm",
      "title": "Prevention of Hepatitis A Virus Infection in the United States: Recommendations of the Advisory Committee on Immunization Practices, 2020",
      "publisher": "US CDC / MMWR Recommendations and Reports (Nelson et al.)",
      "source_type": "govt_report",
      "statistic": "Unvaccinated persons from developed countries traveling to high or intermediate endemicity countries have substantial risk; 97-100% of vaccinated persons aged 2-18 develop protective antibody levels 1 month after first dose; 100% after second dose; >97% of adults remain seropositive 20 years after vaccination; fulminant hepatic failure occurs in <1% of cases.",
      "excerpt": "\"Unvaccinated persons from developed countries who travel to countries that have high or intermediate hepatitis A endemicity have a substantial risk for acquiring hepatitis A. … Hepatitis A remains one of the most common vaccine-preventable diseases acquired during travel. … 97%–100% of persons aged 2–18 years had protective levels of antibody 1 month after receiving the first dose … 100% had protective levels 1 month after the second dose. … Twenty years after vaccination >97% of adults were seropositive for anti-HAV antibodies. … Fulminant hepatic failure is rare and occurs in <1% of cases.\"\n",
      "source_date": "2020-07-03",
      "source_accessed": "2026-05-24",
      "archive_url": "http://web.archive.org/web/20260511185827/https://www.cdc.gov/mmwr/volumes/69/rr/rr6905a1.htm",
      "calculation_notes": "ACIP MMWR 2020 is the primary US policy document on hepatitis A vaccination. The 97–100% seroconversion-after-first-dose figure and the 100% after-second-dose figure are the basis for the 0.03× personal_factor_multiplier for a single dose and the 0.01× multiplier for the full two-dose schedule. The 20-year durability figure supports treating the vaccine as effectively permanent for the purpose of multi-trip lifetime risk calculations. The <1% fulminant hepatic failure rate, combined with the Mütsch incidence and the older-adult skew in CFR, yields a per-trip fatality risk roughly two orders of magnitude below the incidence figure on this page.\n",
      "independence_note": "ACIP MMWR shares CDC upstream with the Yellow Book entry; used here for the vaccine-efficacy and policy-recommendation framing rather than as a second independent incidence estimate. Authors partially overlap with the Yellow Book chapter.\n"
    },
    {
      "url": "https://pubmed.ncbi.nlm.nih.gov/19674261/",
      "title": "Hepatitis A risk in travelers",
      "publisher": "Journal of Travel Medicine (Askling, Rombo, Andersson, Martin, Ekdahl)",
      "source_type": "peer_reviewed",
      "statistic": "Per-100,000 person-month traveler incidence by destination: East Africa 14.1; Middle East 5.8 (18 among unprotected); India and neighboring countries 5.6; North Africa 12 unprotected; East Asia 2 unprotected. VFR (visiting friends and relatives) travelers were 70-91% of cases in high-risk regions; children 0-14 had highest incidence at 3.1 per 100,000.",
      "excerpt": "[Paraphrase from abstract — full text paywalled] \"The incidence of reported hepatitis A in unprotected travelers was 14.1 per 100,000 person-months for East Africa, 18 for the Middle East, 12 for North Africa, and 2 for East Asia. Travelers, and especially children, who are visiting friends and relatives (VFR) in endemic areas constitute a high-risk group for acquiring hepatitis A infection, while the risk for unprotected tourists to East Asia is low.\"\n",
      "source_date": "2009-07-01",
      "source_accessed": "2026-05-24",
      "archive_url": "http://web.archive.org/web/20250204055716/https://pubmed.ncbi.nlm.nih.gov/19674261/",
      "calculation_notes": "Askling et al. is the secondary independent corroboration of the headline figure: a Swedish national surveillance study (separate pipeline from Mütsch's Swiss data) reaching the same order of magnitude. Per-region incidence numbers feed the regional_breakdown rows. The VFR-skew finding and the East-Asia-as-low-risk finding feed the personal_factor_multipliers for destination subregion. The 2 per 100,000 person-month figure for East Asia translates to ~1 per 100,000 per 2-week trip, an order of magnitude below the headline; this is the basis for the 0.1× multiplier on \"East Asia tourist routes\" and contributes to the lower edge of the regional breakdown.\n",
      "independence_note": "Askling et al. uses Swedish surveillance data; methodologically independent of Mütsch's Swiss surveillance and of CDC's US data, though all three rely on the same general framework of laboratory-confirmed imported cases with denominators from tourism statistics.\n"
    }
  ],
  "comparison_anchors": [
    {
      "label": "Travelers' diarrhea per 2-week trip to high-risk destination",
      "lifetime_us_adult": 0.5
    },
    {
      "label": "Typhoid in an endemic country (lifetime, global adult)",
      "lifetime_us_adult": 0.00153
    },
    {
      "label": "Rabies death via dog bite (lifetime, global adult)",
      "lifetime_us_adult": 0.00069
    },
    {
      "label": "Japanese encephalitis per traveler-trip (short-term urban Asia)",
      "lifetime_us_adult": 5e-7
    }
  ],
  "regional_breakdown": [
    {
      "region": "Vaccinated traveler (1 or 2 doses, any destination, any duration)",
      "probability": 0.000002,
      "notes": "ACIP: 97-100% seroprotection after 1 dose, 100% after 2 doses, >97% durability at 20 years. Documented vaccine-failure cases in travelers are rare in the published literature."
    },
    {
      "region": "Unvaccinated nonimmune adult, 2-week trip, intermediate endemicity (e.g. parts of Eastern Europe, Caribbean)",
      "probability": 0.00003,
      "notes": "Lower edge of the Mütsch 6-28 per 100,000 person-month band, applied to a 2-week trip."
    },
    {
      "region": "Unvaccinated nonimmune adult, 2-week trip, high endemicity (South Asia, Sub-Saharan Africa, Mexico, Central America)",
      "probability": 0.00008,
      "notes": "Midpoint of the Mütsch nonimmune-traveler range; matches the headline figure on this page."
    },
    {
      "region": "Unvaccinated nonimmune adult, 2-week trip, East Asia tourist circuit",
      "probability": 0.00001,
      "notes": "Askling et al.: ~2 cases per 100,000 person-months for unprotected travelers to East Asia, an order of magnitude below the headline."
    },
    {
      "region": "Unvaccinated nonimmune long-term traveler or expatriate (1+ month rural, high endemicity)",
      "probability": 0.0005,
      "notes": "Upper edge of Mütsch nonimmune range (28 per 100,000 person-months) scaled to ~1.5+ months. CDC explicitly notes 'cumulative risk for hepatitis A and typhoid fever' justifies vaccination for long-term travelers."
    },
    {
      "region": "Unvaccinated nonimmune VFR (visiting friends and relatives) traveler with children in endemic area",
      "probability": 0.0008,
      "notes": "Askling et al.: VFR travelers represent 70-91% of imported cases in high-risk regions; children aged 0-14 show highest incidence (3.1/100,000 trips, 88% VFR). Reflects food/water exposure in non-tourist settings."
    },
    {
      "region": "Endemic-country susceptible child (for reference — not a traveler figure)",
      "probability": 0.9,
      "notes": "WHO: in low- and middle-income countries with poor sanitation, ~90% of children are infected before age 10. Native exposure anchor, not a traveler risk."
    }
  ],
  "personal_factor_multipliers": [
    {
      "factor": "Full hepatitis A vaccination (2-dose schedule completed)",
      "multiplier": 0.01,
      "notes": "ACIP: 100% seroprotection 1 month after second dose, >97% durability at 20 years. Effectively eliminates per-trip risk."
    },
    {
      "factor": "Single dose of hepatitis A vaccine (≥2 weeks before departure)",
      "multiplier": 0.03,
      "notes": "ACIP: 97-100% seroprotection at 1 month after first dose. CDC accepts a single dose as adequate pre-departure protection for healthy adults <40."
    },
    {
      "factor": "Long-term stay (1+ month) in rural high-endemicity area",
      "multiplier": 5,
      "notes": "Mütsch upper-edge (28 per 100,000 person-months) scaled to multi-month exposure; CDC singles out long-term travelers for cumulative risk."
    },
    {
      "factor": "Visiting friends and relatives (VFR) in endemic area, staying in local households",
      "multiplier": 10,
      "notes": "Askling: VFR travelers 70-91% of imported cases in high-risk regions; non-tourist food/water exposure plus longer typical stays."
    },
    {
      "factor": "Destination is East Asia tourist circuit (Japan/Korea zero-risk; Thailand/Vietnam/Indonesia low)",
      "multiplier": 0.1,
      "notes": "Askling: ~2 per 100,000 person-months for unprotected East Asia travelers, an order of magnitude below the high-endemicity headline."
    },
    {
      "factor": "Age 50+ (incidence unchanged; case fatality and hospitalization risk substantially elevated)",
      "multiplier": 1,
      "notes": "Severity multiplier rather than incidence: CDC reports severe complications and fulminant hepatitis are 'more common in older adults'; 2022 US surveillance shows hepatitis A mortality at 0.15/100,000 in 65+ vs 0.04/100,000 in 45-64. Underlying liver disease compounds this."
    }
  ],
  "short_label": "Hepatitis A (travel)",
  "myth_framing": "calibrated",
  "outcome_severity": "serious_harm",
  "exposure_pattern": "acute",
  "outcome_type": "recoverable_injury",
  "valence": "negative",
  "caveats": "The ~1-in-12,000 figure applies specifically to an unvaccinated, nonimmune adult on a roughly 2-week trip to a high or intermediate endemicity country (most of South Asia, Sub-Saharan Africa, Mexico, Central America, and large parts of South America and the Middle East). Vaccinated travelers face a risk roughly two orders of magnitude lower; visitors to Japan, Korea, Western Europe, North America, Australia, or New Zealand face essentially zero risk regardless of vaccination status. The number is per-trip, not per-adult-lifetime, and is not a substitute for itinerary-specific advice from a qualified travel-medicine clinician. The Mütsch surveillance pipeline counts laboratory-confirmed cases diagnosed after return; mild and asymptomatic infections are systematically undercounted, so the true exposure rate is somewhat higher than the reported case rate — though for symptomatic travel-related illness (the version most readers care about) the published numbers are the relevant ones. This entry measures the risk of contracting hepatitis A, not of dying from it: the overall case fatality rate is <1%, but it climbs to roughly 2% in adults aged 40+ and higher again in people with underlying liver disease, so a per-trip death estimate for an older unvaccinated traveler sits roughly two orders of magnitude below the incidence figure on this page.\n",
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