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Influenza Vaccination Strategies when supply is limited

Influenza Vaccination Strategies when supply is limited. Romarie “Romie” Morales Rosado. Questions. What is the impact of having access only to a limited number of dosages? What is the impact of delays in accessing the available vaccine supply?

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Influenza Vaccination Strategies when supply is limited

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  1. Influenza Vaccination Strategies when supply is limited Romarie “Romie” Morales Rosado

  2. Questions • What is the impact of having access only to a limited number of dosages? • What is the impact of delays in accessing the available vaccine supply? • What is the role of a large percentage of H1N1 asymptomatic infectious individuals?

  3. Type A and its subtypes • Subdivided (H1-H16) , (N1-N9)

  4. Influenza virus and transmission • http://www.youtube.com/watch?v=FvEOjwUOzJc

  5. Impact Pandemic Influenza WHO declared a pandemic in June 2009, a total of 74 countries and territories had reported laboratory confirmed infections. To date, most countries in the world have confirmed infections from the new virus. Source:http://commons.wikimedia.org/wiki/File:H1N1_map_by_confirmed_cases.svg

  6. Confirmed Deaths and Infections Source: http://commons.wikimedia.org/wiki/File:H1N1_map.svg

  7. Pandemic 2009 vs. Pandemic 1918-19Some similarities… • Virus began to appear in the spring. • Came out of nowhere…! • Primarily attack young adults • Elderly were partially immune to 2009 disease Source:http://news.sciencemag.org/sciencenow/2010/03/swine-flu-pandemic-reincarnates-.html?rss=1, http://ent.about.com/od/entdisordersgi/a/H1N1pandemic.htm

  8. Prevention Methods

  9. Methods of Prevention

  10. Importance of Vaccination? • Problem: Not enough vaccines for everyone • Time constraint from identifying virus to creating and approving vaccine • Rich-Poor country Division

  11. Transmission Model P V F S E I J D R Source: G. Chowell et al Addative vaccination strategies

  12. System of nonlinear differential equations

  13. Basic Reproductive Number

  14. Parameters Source: G. Chowell et al Transmission dynamics of the great influenza pandemic of 1918 in Geneva, Switzerland R. Gani, H. Hughes, D. Fleming, T. Grifin, J. Medlock, S. Leach. Potential impact of antiviral use during influenza pandemic. Emerg Infect Dis; 11( 2005); 1355–362. I.M.LonginiJr.,M.E.Halloran,A.NizamandY.Yang.Containingpandemicinfluenzawithantiviralagents. American Journal of Epidemiology; 159(2004); 623–633. C.E. Mills, J.M. Robins and M. Lipsitch. Transmissibility of 1918 pandemic influenza. Nature 432 (2004):904–906.

  15. Cases of Optimal Vaccine Strategies • Limited Vaccine Access • Almost unlimited Vaccine Access • Time Delay

  16. Optimal Control Problem L1 Set of functions –integral of function has finite solution we want u to belong to this set

  17. Unconstraint Vaccine supply case

  18. Sensitivity Analysis • Weight Constant • Control Upper Bound (maximum vaccination rate) • Efficacy of Vaccine

  19. Weight constant

  20. Final epidemic Size when varying Weight Constant

  21. Control upper bound on Final Epidemic Size

  22. Vaccine Efficacy

  23. Isoperimetric Constraint

  24. Recap on Results • Best to apply vaccines at the beginning of the transmission • When transmission is weak a low vaccination policy is effective.

  25. Initial conditions with Delay when R0 = 1.3

  26. Delay R0 = 1.3

  27. Initial conditions with Delay when R0=2

  28. Delay R0 = 2

  29. Results • Maximum Vaccination rate should be applied in a timely manner!!! • No significant difference between unconstrained and constrained cases when R0 is low (1.3) • Increase in vaccine efficacy and upper bound of control results in a decrease in the amount of vaccines that must be administered • Delay has impact on vaccine efficacy.

  30. Future Work • Include asymptomatic class and understand the impact of these individuals on disease transmission .

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