HUMAN CASES AND DEATHS OF H5N1

Worst case scenario

The worst case scenario for a H5N1 pandemic is somewhere around 150,000,000 human deaths directly due to H5N1 infection (or two to three percent of the world's human population). No one knows what the chances are for this worst case scenario.

"Influenza viruses keep changing. They mutate. And they exchange genetic material with other flu viruses, a process called reassortment. All that's needed is a mutation or reassortment that produces a new variant of H5N1 one that's as deadly as the current strain but as easily transmitted from human to human as lots of other flu strains. Most virologists believe something like this will happen sooner or later, and many believe it will happen soon. When it does, H5N1 will inevitably spread throughout the world. Worldwide mortality estimates range all the way from 2-7.4 million deaths (the "conservatively low" pandemic influenza calculation of a flu modeling expert at the U.S. Centers for Disease Control and Prevention) to 1 billion deaths (the avian influenza pandemic prediction of one Russian virologist). The estimates of most H5N1 experts range less widely but still widely. In an H5N1 pandemic, the experts guess that somewhere between a quarter of us and half of us would get sick, and somewhere between one percent and five percent of those who got sick would die the young and frail as well as the old and frail. If it's a quarter and one percent, that's 16 million dead; if it's a half and five percent, it's 160 million dead. Either way it's a big number." Pandemic Influenza Risk.

H5N1 Avian Influenza, Bird Flu. Some developments for a human vaccine.

On August 6, 2005, government scientists at UNIAID, (US National Institute of Allergy and Infectious Diseases), announced results from the first clinical trials of a vaccine being developed to protect humans against H5N1 avian influenza ( bird Flu ). Preliminary tests show that the experimental vaccine evoked an immune response in a small group of healthy adults.

Although more tests are needed, this is at least a good sign that developing a H5N1 specific vaccine is possible.

Currently it is believed that the next pandemic will be caused by the H5N1, Avian Influenza ( bird flu ) virus. The increasing spread of the H5N1 virus, especially in asia, have brought the world much closer to to another pandemic then at any time since 1968, when the last of the 1900's three pandemics began.

Vaccines are the main ammunition in the fight against pandemic influenzas, especially ones of the Avian Influenza (bird flu) type. If available to the public in a timely manner and in great enough quanities they can reduce the morbidity and mortality that have traditionally made pandemics such socially disruptive as well as deadly events.

However many obstacles need to be overcome before vaccines can even help alleviate some of the effects of the next pandemic.One of, if not the most important is to find vaccine formulations that make the greatest use of the limited supply of antigens we have.

Antigen is the component of the vaccine that elicits an immune response. The US trial provides important insight into possible vaccine formulations. It used doses that are higher than the amount of virus antigen contained in influenza vaccines produced yearly for normal seasonal epidemics.

Strategies for stretching limited antigen supplies

By adding an adjuvant to the vaccine formulation or injecting the vaccine into the skin rather than into muscle, have been proposed. Adjuvants are chemicals that can be added to the vaccine formulation to boost the immune response, theoretically allowing the use of smaller doses of antigen to achieve an immune response. Such antigen-sparing strategies using adjuvants are currently being tested by several manufacturers, and preliminary results are expected within the next three months.

At present, 90% of production capacity for all influenza vaccines is concentrated in Europe and North America in countries that account for only 10% of the world�s population. Current global manufacturing capacity (estimated at 300 million doses of regular trivalent influenza vaccine per year) is inadequate to meet the expected global needs during a pandemic and cannot be rapidly augmented.

Influenza pandemics are unique infectious disease events that can spread to every country in the world within months, resulting in a high and universal demand for preventive and treatment measures. Pandemics thus throw into sharp relief inequities in global access to vaccines and other medical interventions during an emergency. Based on past experience, countries with local manufacturing capacity are likely to meet domestic demand for vaccines and other critical resources fully before freeing supplies for the export market.

Because the present total global manufacturing capacity for influenza vaccine is limited, any decision to manufacture a pandemic vaccine in large quantities prior to the start of a pandemic would, of necessity, compromise the capacity to produce vaccines for seasonal influenza. Seasonal epidemics of influenza predictably cause an estimated 250,000 to 500,000 deaths each year. In the current situation, the capacity to respond to seasonal influenza must be balanced against preparations for pandemic influenza. However, once a pandemic has been declared, all manufacturers would stop production of seasonal vaccines and produce only the pandemic vaccine.