The International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) has estimated that a pandemic could make vaccine demand rocket to 20 times the 300 million doses that are administered annually worldwide.
Current worldwide capacity is estimated at less than 400 million doses per year of trivalent seasonal influenza vaccine.
Meeting the increased demand would prove a significant logistical challenge in terms of manufacture and distribution.
In an attempt to address this problem, last year the WHO launched the global pandemic influenza action plan to increase vaccine supply, an effort costing $10bn over 10 years. Considering influenza epidemics were recently estimated to cost the $71-167bn in health care costs and lost productivity in the US alone, the money will be well spent if the programme succeeds.
At a WHO meeting in Geneva last week, experts reported promising progress on the development of new pandemic influenza vaccines. Particularly highlighted were efforts by manufacturers to produce vaccines to protect against avian influenza viruses, with encouraging results from clinical trials.
Sixteen manufacturers around the world are currently in the process of developing prototype pandemic influenza vaccines against the H5N1 avian flu virus, with six of them also involved in developing vaccines against other avian flu strains as well.
Clinical trials conducted on potential pandemic vaccines have shown that in order to achieve similar immune responses to those stimulated by seasonal flu vaccines, the vaccines have to be adapted slightly in comparison to the familiar seasonal jabs.
For example, trials have shown that multiple doses of the vaccine are required instead of the usual single vaccination common with seasonal flu vaccines, a higher antigen content is also required and/or the use of an adjuvant.
Results presented at the Geneva meeting "convincingly demonstrated that vaccination with newly developed avian influenza vaccines can bring about a potentially protective immune response against strains of H5N1 virus."
All the companies highlighted by the WHO involved in developing avian flu vaccines are using adjuvants in their vaccine formulations, although Crucell's Berna Biotech is using a virosome approach to provide a combined carrier-adjuvant system.
The majority of the vaccines under development target one specific strain of influenza virus, although one company, Merck & Co., is focusing on developing a universal influenza vaccine.
Delivery systems being researched by the manufacturers include both subcutaneous and intramuscular injection, while US based MedImmune is developing a nasal spray formulation to protect against the H5N1 virus.
Over 40 clinical trials have been completed or are currently ongoing, most focusing on healthy adults, although Australian firm CSL has initiated trials with young children and the elderly and Sanofi Pasteur also has trials ongoing for vaccines for the elderly.
The H5N1 strain of avian flu has spread to more than 40 countries, and has infected over 270 people across the world killing over 160. A fresh outbreak is currently being reported on the outskirts of Moscow, with cases of the H5N1 virus having been confirmed in five districts, and suspected in two more.
Although currently primarily an animal disease, experts fear that the virus could mutate, acquiring the ability for sustained transmission among humans. This could potentially trigger a flu pandemic, which would have grave consequences for global public health and put millions of lives at risk.
