Pandemic preparedness: What can epidemiological modelling offer policy?

1. Pandemic preparedness:What can epidemiological modelling offer policy? Nim Arinaminpathy Department of Zoology University of Oxford

2. Talk plan • Influenza: a background • From today to emergence of a novel influenza virus • Antiviral drugs for control of pandemic influenza

3. Influenza • RNA virus • Clinical manifestations: Headache, sore throat, chills, fever, myalgia, anorexia, malaise • Transmission By contact with respiratory droplets, generated by coughing or sneezing • Infectiousness can start a day before symptoms and continue for 3 – 5 days after symptoms developing in adults

4. The seasonal influenza burden • Disease: • 5 – 15% of population affected with upper respiratory tract infections in annual ‘flu season • Estimated 3-4,000 annual deaths in UK caused by influenza infection (mainly elderly and immunocompromised) • The Economy: • Europe: flu accounts for ~10% of sick leave • Costs US estimated $90bn a year

5. Influenza family tree Orthomyxoviridae … Influenza From http://www.abc.net.au/health Type A B C … Subtype H1N1 H3N2

6. Pandemic and seasonal influenza Taken from www.en.influenza.pl

7. Social and economic disruption

8. Social and economic disruption

9. H5N1: Future pandemic? • Wild bird reservoir  Poultry  Humans • Transmitted from bird to human by inhaling dried aerosolised faeces • First major outbreak in 1997, Hong Kong • Resurgence in 2003 has seen virus established in poultry in South-East Asia • So far human-to-human spread is non-existent or very limited • 387 human cases, 245 deaths to date • Wide geographical spread, from S.E.Asia (inc. Indonesia, Viet Nam) to Africa (Nigeria, Egypt) • However, H7N7 and N9N2 are also pandemic candidates

10. Evolution and emergence of pandemic influenza • Each human case is an opportunity for an avian virus to adapt for human transmission

11. Antiviral drugs for pandemic control • No vaccine for at least first 6 months • Oseltamivir (Tamiflu) is main antiviral drug of choice • UK stockpile: • Currently enough for 25% of population • Drugs intended mainly for treatment, not prophylaxis • For all clinical cases • How best to minimise epidemic size and impact with a limited stockpile?

12. A simple compartmental model γT αλ IT RT S γN (1-α)λ IN RN

13. A simple compartmental model γT αλ IT RT S γN (1-α)λ IN RN

14. 1957 ‘Asian Flu’ pandemic 30/11/57 22/02/58

15. 1957 ‘Asian Flu’ pandemic

16. 1957 ‘Asian Flu’ pandemic

17. 1957 ‘Asian Flu’ pandemic CFR 0.16% R0 1.65 25% stockpile exhausted

18. How many drugs are needed? ‘Secondary’ effect of mass antiviral treatment is to reduce the spread of infection in the community Its strength depends on drug efficacy and disease transmissibility

19. Antiviral programmes • By shortening infectious period and reducing infectiousness, antiviral drugs can influence the course of infection • Broadening and delaying epidemic peak • Reducing numbers of cases • If there is a risk-group for whom the drug has little protective effect, the stockpile is better deployed in the general population. • Priority shifts to protection from infection rather than from illness.

20. The ‘social element’ • Potential wastage of drugs on the ‘worried well’ • Personal stockpiles • Non-compliance with treatment regime may lead to drug resistance • Pressing ethical questions, eg distributive justice

21. Conclusions • Mathematical models can offer valuable insights into disease control • Transmission dynamics are often fundamental to epidemic outcomes and effects of interventions • …sometimes offering counterintuitive results! • However models always entail simplifications, often about human behaviour (important factors) • Effective pandemic preparedness could involve a synergy between such models and the social sciences