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Theo Knight-Jones, S. Gubbins, A.N. Bulut, K.D.C. Stärk, D.U. Pfeiffer,
K.J. Sumption and D.J. Paton
Annual meeting of the...
When there is an ongoing threat FMD control is often
based on mass vaccination
- ≥3PD50 vaccines typically used
- Much low...
Mass vaccination twice a year:
Population age-sex-vaccination distribution
Beef suckler cattle:
Percentage of population
Mass vaccination twice a year:
Population age-sex-vaccination distribution
Beef fattener cattle:
9-10 doses
7-8 doses
5-6 ...
Robinson et al., 2011. Global livestock production systems. Rome, Italy: FAO and Nairobi, Kenya: ILRI
Density of rural poo...
Population vaccine history & immunity varies by region
Thrace FMD free with vaccination
Anatolia high FMD incidence
Differ...
Age-structure changes with births & deaths
over the annual production cycle
New births = New unvaccinated animals
Populati...
Post-vaccination immunity declines with time
Vaccinated
Spring 2012
+Autumn 2012
Vaccinated
Autumn 2011+
Spring+Autumn
201...
If 3 doses needed for “adequate” protection
If multiple doses needed, variation in the percentage
adequately vaccinated be...
• Described population vaccine immunity over the
2012 annual production cycle in Anatolian Turkey
• Vaccinated every six m...
Percentage never vaccinated, 6 months after mass vaccination
– if all eligible cattle always vaccinated
Unvaccinated = Cat...
Vaccinated ≥3 times = Adult cattle
Percentage vaccinated ≥3 times in lifetime
– if eligible cattle always vaccinated Best ...
Field studies and routine data found 40–100% vaccinated
But not all eligible cattle will be vaccinated
Results:
• Six mont...
• Using regression models fitted to data from
extensive post-vaccination sero-monitoring study
[n=647]
• Predict immunity ...
Population immunity predictions
Primary courseAutumn mass
vaccination
Two-dose primary course:
Increases proportion of
6-1...
District coverage and population immunity
Modelled proportion vaccinated in a district at autumn vaccination against the p...
Sustained antibodies after single dose
From: Selman P, Chénard G, Dekker A (2006) Cedivac-FMD; Duration of Immunity in cat...
• Major immunity gaps despite biannual mass vaccination
• Improved vaccines required
• Prioritise repeat vaccination of yo...
Knight-Jones, T. J. D. et al. Sci. Rep. 6, 22121; doi: 10.1038/srep22121 (2016)
www.researchgate.net/profile/Theodore_Knig...
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Mass vaccination, immunity and coverage: Modelling population protection against foot-and-mouth disease in Turkish cattle

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Presentation by Theo Knight-Jones, S. Gubbins, A.N. Bulut, K.D.C. Stärk, D.U Pfeiffer, K.J. Sumption and D.J. Paton at the annual meeting of the Society of Veterinary Epidemiology and Preventive Medicine, Elsinore, Denmark, 16-18 March 2016.

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Mass vaccination, immunity and coverage: Modelling population protection against foot-and-mouth disease in Turkish cattle

  1. 1. Theo Knight-Jones, S. Gubbins, A.N. Bulut, K.D.C. Stärk, D.U. Pfeiffer, K.J. Sumption and D.J. Paton Annual meeting of the Society of Veterinary Epidemiology and Preventive Medicine Elsinore, Denmark, 16-18 March 2016 Mass vaccination, immunity and coverage: Modelling population protection against foot-and-mouth disease in Turkish cattle
  2. 2. When there is an ongoing threat FMD control is often based on mass vaccination - ≥3PD50 vaccines typically used - Much lower potency than vaccines used in EU outbreaks - Require several doses for adequate immunity - Immunity declines with time since vaccination Mass vaccination Mass vaccination Population immunity ≈ Population vaccination history [No. of doses, time since last dose] Population vaccination history ≈ Population age structure
  3. 3. Mass vaccination twice a year: Population age-sex-vaccination distribution Beef suckler cattle: Percentage of population
  4. 4. Mass vaccination twice a year: Population age-sex-vaccination distribution Beef fattener cattle: 9-10 doses 7-8 doses 5-6 doses AgeFemales 4-5 years 3-4 years 2-3 years 1-2 years 0-1 years Males Percentage of population Females Different production system = different age structure = different population immunity
  5. 5. Robinson et al., 2011. Global livestock production systems. Rome, Italy: FAO and Nairobi, Kenya: ILRI Density of rural poor livestock keepers
  6. 6. Population vaccine history & immunity varies by region Thrace FMD free with vaccination Anatolia high FMD incidence Different production system = different age structure = different population immunity
  7. 7. Age-structure changes with births & deaths over the annual production cycle New births = New unvaccinated animals Population immunity is constantly changing with population turnover & declining antibodies
  8. 8. Post-vaccination immunity declines with time Vaccinated Spring 2012 +Autumn 2012 Vaccinated Autumn 2011+ Spring+Autumn 2012 Protection threshold Antibodies against FMD Structural proteins once twice 3 times 2.3 2.4 2 0 Log10 (SP titre) Autumn mass vaccination Vaccinated Once Autumn 2012 depending vaccine history
  9. 9. If 3 doses needed for “adequate” protection If multiple doses needed, variation in the percentage adequately vaccinated becomes exaggerated District with 100% coverage: After 3 rounds: 100% of eligible cattle vaccinated 3 times District with 50% coverage: After 3 rounds: 50% x 50% x 50% = 12.5% vaccinated 3 times Clustering of husbandry+age-structure+compliance+competence => Reservoirs of susceptibility With six-monthly vaccination animals will not reach 3 doses until >18 months old
  10. 10. • Described population vaccine immunity over the 2012 annual production cycle in Anatolian Turkey • Vaccinated every six months, spring/autumn (≥3PD50 vaccine) • Single-dose primary course (not two-dose/prime-boost) Population coverage model - Anatolia • Simulated the Turkish cattle population for each province • Using data from national random surveys and census data • Dynamic population model representing the changing age structure for each province over the annual production cycle
  11. 11. Percentage never vaccinated, 6 months after mass vaccination – if all eligible cattle always vaccinated Unvaccinated = Cattle too young at prior vaccination + New births since prior vaccination median values reported Best case scenario
  12. 12. Vaccinated ≥3 times = Adult cattle Percentage vaccinated ≥3 times in lifetime – if eligible cattle always vaccinated Best case scenario FMD extremely infectious R0 2-70
  13. 13. Field studies and routine data found 40–100% vaccinated But not all eligible cattle will be vaccinated Results: • Six months after the last round of vaccination almost half of the cattle aged ≤24 months remain unvaccinated Betapert distribution (minimum=40%, maximum=100%, most likely=80%) • Only 50% of all cattle would have been vaccinated more than once with the last dose received ≤6 months ago
  14. 14. • Using regression models fitted to data from extensive post-vaccination sero-monitoring study [n=647] • Predict immunity for simulated population Antibody titre = Time since vaccination + No. of times vaccinated (LPBE SP) From coverage to immunity
  15. 15. Population immunity predictions Primary courseAutumn mass vaccination Two-dose primary course: Increases proportion of 6-12 month cattle above threshold by 25-40% Log10 (SP titre) ≥2: 32% [25%-40%] Log10 (SP titre) ≥ 2: 27% [20%-35%] Log10 (SP titre) ≥ 2: 30% [24%-38%] Log10(SP titre)
  16. 16. District coverage and population immunity Modelled proportion vaccinated in a district at autumn vaccination against the percentage of cattle with a serotype O SP titre ≥1:102 in mid February Log10(SP titre)≥2 ≈ 70% protection against the vaccine strain Threshold titre is useful but Titre ≈ Protection Antigenic similarity of: 1) Vaccine – 2) Field virus – 3) Test %Log10(SPtitre)≥2 Even super-vets struggle given limitations of vaccine and presence of young cattle
  17. 17. Sustained antibodies after single dose From: Selman P, Chénard G, Dekker A (2006) Cedivac-FMD; Duration of Immunity in cattle, sheep and pigs. Open session of the EuFMD, Paphos, Cyprus, 17-19 October 2006 - Need rapid, sustained immunity after a single dose
  18. 18. • Major immunity gaps despite biannual mass vaccination • Improved vaccines required • Prioritise repeat vaccination of young animals • ≥6PD50 vaccine now routine in Turkey • Two-dose primary course now used • Accompanied by reduction in reported outbreaks 1000 outbreaks in 2013 - 253 in 2014 - 263in 2015 • Immunity gaps will still exist • Each round of vaccination may exclude a quarter of all cattle • Vaccinated population susceptible to poorly matched strains • Improved biosecurity measures required • Avoid over reliance on vaccine protection • Easier said than done in smallholder systems dependent on communal grazing • Can FMD be controlled using high potency vaccines with minimal biosecurity? Conclusions: Mass vaccination in Turkey 2012
  19. 19. Knight-Jones, T. J. D. et al. Sci. Rep. 6, 22121; doi: 10.1038/srep22121 (2016) www.researchgate.net/profile/Theodore_Knight-Jones

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