The slides are from a keynote presentation delivered by ASTMH Secretary-Treasurer David R. Hill, MD, DTM&H, FRCP, FFTM, FASTMH at the 2013 Annual Conference of New Zealand Society of Travel Medicine in Wellington, NZ, 3 August - 4 August.

1. Yellow Fever: Risk Mapping
Wellington, August 2013
David R Hill MD DTM&H FRCP FFTM FASTMH
Professor of Medical Sciences
Director, Global Public Health
Frank H Netter MD School of Medicine
Quinnipiac University

2. Assessing Geographic Risk of Yellow Fever
• Defining disease risk in travellers
• Goals, rationale and process
• Outcomes: new categories of risk
• Specific country examples
• Implications: travel medicine & IHR (2005)
• Implementation

3. • For relatively high incidence disease we combine:
 global epidemiology of disease
 imported cases / # travellers / destination / time
Defining Disease Risk for Travel

4. Defining Disease Risk: Malaria
US Civilian Travellers, 2008
Mali S, et al. MMWR
59(SS-7):1, 2010
Travellers Visiting Friends and Relatives:
3.7 x  risk to West Africa Smith AD, et al. BMJ 337:a120, 2008

5. • Enteric fever imported to UK:
 93% of cases from South Asia
Defining Disease Risk: Enteric fever
UK Travellers
Country
Rate*
VFR
Rate Non-
VFR
India 28.8 3.3
Pakistan 26.4 8.2
Bangladesh 36.9 10.5
* Rate of S. Typhi and S. Paratyphi A/100,000 visits
Lawrence J, Jones J. Enhanced enteric fever surveillance.
UK Public Health England, 2008.

6. • For low volume disease we take into account:
 global epidemiology (geography of risk)
 severity of disease
 case reporting becomes anecdotal
• Polio, Japanese encephalitis, yellow fever
• Define risk based on geography and exposure
Defining Disease Risk for Travel
Base prevention on sensible,
‘evidence-based’ measures

7. Imported Yellow Fever Cases: 1970-2013
Country Year Case Outcome Vaccinated?
Senegal 1979 42, M Death No
Senegal 1979 25, M Death No
Guinea-Bissau 1985 27, F Survived No
West Africa 1988 37, F Survived Yes
Brazil 1996 53, M Death No
Brazil 1996 42, M Death No
Cote d’Ivoire 1999 40, M Death No
Venezuela 1999 48, M Death No
The Gambia 2001 47, F Death No
Brazil 2002 47, M Death No

8. 2011 WHO Yellow Fever
Vaccination Maps
Vaccination recommended
Vaccination usually not recommended
Not recommended

9. Historical Determination of YF Risk
• Clinical case reports
– severe illness, foreigners,
coastal ports, rivers and railways
– non-specific: e.g. confused with
malaria, hepatitis, leptospirosis
• Serosurveys: mouse protection
assay (1931)
• Viscerotomies in persons dying
with a febrile illness; mostly in
S. America

10. Yellow Fever Epidemiology: Africa
Sawyer WA. Harvey Lectures. 66-92, 1936.
Human Cases: 1920-1934 Human Serology: 1930-1934

11. Yellow Fever Endemic Regions, 1945
UN Relief and Rehabilitation Administration. Epidemiol Inf Bull. 1:687, 1945.
South America Africa

12. • Response to:
– recognition of serious adverse events
– changing epidemiology of yellow fever
• Goals:
– more accurate definition of risk areas
– unify risk maps between CDC & WHO
– transparency of recommendations
– inform country policy around IHR (2005)
WHO Consultation on Yellow Fever Risk, 2008
Jentes E, et al. Lancet Infect Dis. 11:622, 2011
Curr Infect Dis Rep 14:246, 2012

13. Evidence Used for Risk Mapping
• Human and non-human primates: cases,
clusters and outbreaks
• Human serology prior to YF vaccination;
most data generated in 1950s and earlier
• Vegetation and altitude
• Vector distribution

14. Kenya: Yellow Fever Serology and Cases
Courtesy Tom Monath

15. PAHO: July 2010
South America: Altitude limit of 2,300 m

16. Regional land cover:
Horn of Africa

17. • Endemic
• Transitional
• Low potential (risk)
for exposure
• No risk
Yellow Fever Consultation
Creation of New Categories of Risk

18. Yellow Fever Risk Classification
Risk
Classification
Examples
Criteria for Risk
YF vectors
and NHP
present?
Human or
NHP YF
cases?
Serosurvey
evidence?
Endemic Nigeria Yes Repeatedly High levels
Transitional Paraguay Yes
Reported at
long intervals
Present
Low potential
for exposure
Tanzania Yes None Low levels
No New Zealand Yes / No None No

19. Use of Elevation Data: Bolivia
Areas below 2,300 m, determined from
global digital elevation model (GTOPO30 )
Areas below 2,300 m classified endemic
Altitude limit of 2,300 m

20. Use of Vegetation Data: Niger
Barren or sparsely vegetated areas
as determined from normalized
difference vegetation index (NDVI)
Areas classified as endemic

21. Peru:
 no risk: coastal, south of La
Libertad, Andes above 2,300 m
 low potential: Tumbes,
Lambayeque, and parts of
Piura and Cajamarca
 transitional: eastern Piura state
 endemic: remainder of country
New Yellow Fever Risk Maps

22. Kenya:
 low potential: North
Eastern zone, Coastal
zone and Nairobi
 endemic: remainder of
country
New Yellow Fever Risk Maps

23. Tanzania
 low potential
for exposure
New Yellow Fever Risk Maps

24. Zambia
 low potential: North
West and Western
provinces
 no risk: remainder
of country
New Yellow Fever Risk Maps

25. Special Considerations
• Examined high volume destinations, in attempt to
avoid vaccinating many travelers unnecessarily
• Low potential for exposure:
 port cities in South America
 Cartagena, Baranquilla, Port of Spain
 Nairobi
• No risk:
 transit of 12 h or less in international airports
 Inca Trail (Peru)

26. Yellow Fever Risk Mapping:
Shift from risk maps to vaccination maps
• Vaccination recommended
– endemic
– transitional
• Vaccination generally not recommended
– low potential for exposure (low risk)
– exceptions: prolonged, often rural,
extensive mosquito exposure
• Vaccination not recommended
– no risk

27. Risk
Vaccination recommended
Vaccination usually not recommended
Not recommended
Vaccination

28. Implications for IHR (2005)
Low risk countries

Low potential for exposure
Thus, low risk countries will never appear in Annex 1


29. IHR (2005): Annex 1B, 2f
Afghanistan, Australia, & India require YF vaccine
from travellers arriving from countries with a (low) risk
of YF transmission; e.g. historically from Tanzania,
Eritrea, Zambia.
South Africa considers ‘low potential’ as risk and
requires vaccine of travelers from Tanzania &
Zambia, including those in transit.

30. 2011 WHO Yellow Fever
Vaccination Maps
Vaccination recommended
Vaccination usually not recommended
Not recommended

31. http://www.who.int/ith/en/

32. Conclusions
• Robust process using best available evidence
• Transparency in decision making
• Attempts at ‘shrinking’ risk map
• Achieved globally agreed risk categorization
• Implications for travel medicine practitioners
• Implications for Annex 1 (ITH) under IHR (2005)
• Continuous review of model and epidemiology