Human infections with avian flu strain H5N1 are occurring in a number of southeast Asian countries that have experienced large
outbreaks of avian influenza. How great a risk to the human population is posed by this virus, and what steps can be taken
to minimize its impact? Preventive vaccines have great potential to avert the spread of avian flu and other infectious diseases.
What are the factors affecting the creation of new vaccines, and how can they be optimized to promote public health?
Michael J. Shuster, J.D., Ph.D
RISKS POSED BY H5N1
Human infection with avian H5N1 virus was first noted in Hong Kong in 1997. Of eighteen people known to be infected, six died.
All of the infected people had close contact with domestic birds.1 Data suggest that human-to-human transmission of H5N1 is extremely inefficient, and that avian flu cannot currently be
spread among people by coughing or sneezing (small particle aerosol transmission).2 Instead, transmission to people results from direct con-
tact with infected poultry, although infection through environmental exposure, such as to contaminated water, also seems possible,
given the survival of H5N1 in the environment.3 Both the popular press and scientific literature have debated the possibility of mutations occurring in the H5N1 virus,
allowing it to more easily spread among people.
Experts believe that if H5N1 were to mutate to a more easily transmissible form, the mortality rate would not be as extreme
as that of the 1918 pandemic in countries that have mechanisms to control the spread of the disease, as well as the ability
to treat it. The 1918 flu pandemic occurred during World War I, which exposed many people to unsanitary conditions that promoted
the spread of disease.
However, in the worst case scenario, the human-to-human spread would pave the way for pandemic infection, such as the influenza
pandemics of 1918, 1957, and 1969. As the debate continues, it is clear that the risk must be taken seriously, and that we
must start preparing for a possible avian flu pandemic now.
The US government has appropriated $7 billion to prepare for the threat of an avian flu pandemic, earmarking funds to treat
infected populations, contain outbreaks, and — most importantly — prevention. H5N1 currently can be treated with neuraminidase
inhibitor drugs such as Roche's oseltamivir (Tamiflu), and clinical trials are under way for BioCryst's neuraminidase inhibitor
Peramivir. But there have been reports of resistance to this type of drug therapy.2 Government stockpiling of effective antiviral agents and other first-line patient care necessities, such as ventilators,
is an important component of the response. Tamiflu is a scarce resource, leading some policy makers to suggest compulsory
licensing of Roche's patents on the drug as a way to alleviate the shortage. While the limited amount of the raw ingredient
used to produce Tamiflu is considered an impediment to increased manufacture, there is another reason to reject compulsory
licensing.€It threatens to rob pharmaceutical companies of the returns they need to support their R&D investments that produce
other innovative products.4
Vaccine development holds the greatest promise of protecting the worldwide population from an avian flu pandemic. Two experimental
vaccines (manufactured by Sanofi-Aventis and Chiron) against H5N1 are in clinical trials sponsored by the National Institute
of Allergy and Infectious Disease. Both vaccines are made from inactivated H5N1 viruses.5 While early results have been encouraging, many challenges remain.6
INCENTIVIZING VACCINE DEVELOPMENT
The ability to use a vaccine to prevent a pandemic hinges on developing a safe and effective vaccine to protect against infection,
and on the percentage of the at-risk population that becomes vaccinated. Vaccines are administered to healthy individuals
to protect against an uncertain risk. These individuals are unlikely to take a vaccine if they perceive that their risk of
falling ill from the infection is less than the risk of being harmed by the vaccine. Concerns about their ability to recover
economic damages arising from vaccine-induced harm further reduce the propensity of many individuals to be vaccinated. On
the other hand, vaccine manufacturers are unlikely to undertake the economic and technical burdens associated with creating
a vaccine if they perceive that an insufficient market exists or that liability exposure reduces their ability to earn a fair
return on their investment.