Pandemic Influenza: History & Epidemiology

1. Pandemic Influenza: History & Epidemiology Kathryn H. Jacobsen, MPH, PhD Dept. of Global & Community Health George Mason University

2. What is “normal” flu? • Respiratory disease • Symptoms: fever, muscle aches, cough, sore throat, runny nose, and possible nausea • May develop into pneumonia • Spread by airborne droplets that reach the eyes, nose, or mouth; may also be spread by touching contaminated surfaces and then the face • The elderly, very young, and those with weakened immune systems are at risk of severe illness (especially pneumonia) and death. • 30,000 – 40,000 deaths in the USA in a “normal” flu year (and 5 – 20% of the population sick)

3. Why are we susceptible to new flu strains?: Antigenic Drift • Influenza viruses frequently mutate (antigenic drift). • Surface proteins change in ways that make it difficult for our immune systems to quickly identify them and fight them off. • A new flu vaccine is developed every year to adjust for the changes in the circulating flu viruses.

4. Why are we susceptible to new flu strains?: Antigenic Shift • Two very different types of flu virus that infect one animal can merge to create a completely new strain (antigenic shift). • Most common strain in humans in recent decades: H3N2 • “Bird flu”: H5N1 Domestic birds Domestic pigs Humans

5. What is “bird flu”? • Many flu strains are “bird flu” or “pig flu”, etc. • Avian influenza H5N1 is a flu virus type that primarily affects birds; highly contagious in birds and has resulted in many bird deaths • Bird flu is “species specific” and rarely infects humans; only a few hundred humans are known to have contracted H5N1 • Genetic changes may cause H5N1 to develop the ability to more easily infect humans Domestic birds Domestic pigs Humans Wild birds

6. Why are we concerned about H5N1? • Most humans have no immunity to H5N1 • About half of the humans known to have been infected with H5N1 have died. • Important note: This is an overestimation of the true case fatality rate because only severe cases are tested. • All had direct and prolonged contact with poultry or bird habitats. • Most cases have occurred in children and young adults.

7. Why are we concerned about a possible pandemic? • Conditions for a pandemic • (1) Emergence of a new flu strain • (2) Ability of the strain to infect humans and cause severe illness • (3) Ability to spread easily among humans • If further mutations of the H5N1 virus occur and the virus becomes easy to transmit from human to human a global outbreak (pandemic) could occur.

8. WHO Pandemic Staging • Interpandemic Period • Phase 1 – Low Risk: No new influenza virus subtypes in humans • Phase 2 – New Virus: No new flu in humans but an animal variant emerges • Pandemic Alert Period • Phase 3 – Self Limiting: Human infections but no human-to-human transmission • Phase 4 – Person-to-Person: Small clusters with limited human-to-human transmission • Phase 5 - Epidemic: Larger but still localized clusters • Pandemic Period • Phase 6 - Pandemic: Increased and sustained transmission in the general population

9. Pandemics (Global Epidemics) in History • 541 CE, bubonic plague spreads from Egypt to Constantinople then beyond, killing up to ¼ of the population of the eastern Mediterranean • 1300s CE, bubonic plague (“Black Death”) returns to Europe from Asia and kills up to ¼ of the population (and more than half in the hardest hit areas) • 1500s CE, typhus pandemics; Europeans bring smallpox and other epidemic infections to the Americas • A series of cholera outbreaks in the 1800s hit all continents

10. Pandemic Influenza History • 1580: Africa  Europe • 1729: Russia  Europe • 1781-1782: China  Russia  Europe • 1830-1833: China  Pacific and India  Russia  Europe • 1889-1900 “Asiatic flu”: Russia  Mediterranean  North America  South America  India and Australia • 1918-1919 “Spanish flu”: Started in October 1918, quickly spread worldwide, and vanished within 18 months • 1957-1958 “Asian flu” • 1968-1969 “Hong Kong flu” Potter CW, A history of influenza, Journal of Applied Microbiology 2001; 91: 572-579.

11. Why are we concerned about a possible pandemic? • Modern influenza pandemics tend to occur every 20 to 30 years ?

12. Where is H5N1 now? Nations With Confirmed Cases H5N1 Avian Influenza (July 7, 2006) http://www.pandemicflu.gov/

13. How quickly will it spread? • It may take several weeks for an initial outbreak to be announced • Influenza may be found in dozens of countries within a week or a few weeks • Travel advisories and warnings may be issued quickly and restrict international travel and/or local travel • Quarantine orders may be issued within weeks • Thousands to millions may become infected

14. Sample Timelines

15. Sample Timelines

16. How can we respond to H5N1? • A flu vaccine might be developed – but probably not in time to prevent a pandemic because human-to-human transmissible H5N1 does not yet exist. • Production capacity may also be an issue. • Antiviral drugs that mitigate symptoms (like Tamiflu and Relenza) may not work against this strain. • We do know that normal preventive measures will be helpful in preventing transmission. • We can plan!

17. Areas of Concern Addressed during Today’s Conference • Clinical features of H5N1 • Comparisons to other EIDs like SARS • Planning, security, communications, and preparation