28 August 2007
This is from a recent Continuing Medical Education Course I completed in August 2007, put on by Annenberg Center for Health Sciences and sponsored by the Dept of Defense
- All known Influenza A types circulate in wild birds. Wild birds serve as a reservoir for the virus strains and a source of infections in domestic birds and humans
- Influenza Type A/H5N1 is new to humans, first cases in 1997. Infections generally from very close contact with infected fowl or their fecal or mucosal matter.
- Deaths generally occur from respiratory complications which can occur within days of initial infection.
- Since 2003, human cases have produced mortality rates exceeding 50%, in some outbreaks 75% to 100%.
- Confirmed cases are growing in number and are spreading in geographic origin.
- H5N1’s transmissibility from human to human has already been documented, but, thus far has been exceedingly rare.
- Spanish Flu of 1918 is the pandemic by which others are measured.
- 20 to 50 million deaths worldwide, 550,000-675,000 in the US resulting in a drop of 10 years of life expectancy for the entire US in 1918
- Studies in mice and ferrets (who have susceptibility to influenza most similar to humans) have shown H5N1 viruses to be more lethal than the 1918 flu virus.
- The only positive is that thus far the H5N1 viruses have not been easily transmitted from human to human. Rapid and sustained person-to-person transmission is but ONE genetic change away.
- A new pandemic would be unpredictable, might not always occur in winter
- Rapid surge in cases would occur in brief time, often a matter of weeks and occur in waves with each wave being more or less severe than the previous.
- Since a considerable proportion of the population will require medical attention, the need for health care personnel, public health involvement, disaster planning, respirators, hospital beds, equipment and isolation wards may quickly and greatly exceed the supply. Think New Orleans after the hurricane on a world wide basis.
- There may be inevitable major societal disruptions (closings of schools and businesses, interruptions of public transportation and delivery of food and goods to market)
- Infection Control – isolating cases and outbreaks, and perhaps using masks
- Monitoring incoming travelers and possibly limiting travel/border closures
- Using antiviral agents for therapy and prophylaxis
- Culling bird reservoir populations
- Most virologists think another pandemic will occur quickly and that a vaccine will not be available for 6 to 9 months after the initial outbreak
- Even when a vaccine is available, if it works like current Influenza A vaccines, it will only be 57% to 77% effective
- Whole virus vaccines are more effective but currently NO vaccine manufacturer is set up to manufacture whole virus vaccines.
- Four drugs available:
- Amantadine (Symmetrel)
- Rimantadine (Flumadine)
- Oseltamivir (Tamiflu)
- Zanamivir (Relenza)
- Treating patients
- Prophylaxis for essential medical/LEO/military/government personnel and exposed family members
- Treating the healthy to decrease spread of virus
- Studies have shown zanamivir up to 81% effective in preventing Influenza infection compared to placebo
- Studies have shown reduction of duration of illness by 26% with oseltamivir but have NOT shown a definite reduction in serious respiratory complications (antivirals MAY NOT reduce high mortality rates in already infected individuals)
- Drug Resistance has become a major concern – Amantadine and Rimantadine resistance is increasing in frequency and they are now NOT recommended during an Influenza epidemic
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