The Flu Disease
The flu disease is an acute respiratory tract infection characterized by fever, rhinitis, coughing, headaches and malaise. The incubation period ranges from 1-5 days, with an average of 2 days. Flu patients are more vulnerable to other infections, with the most common complication being pneumonia. During any particular influenza season, the virus may infect 5%-20% of the entire population.
The influenza A viruses are responsible for about 80% of influenza illnesses, resulting in many millions of infected individuals worldwide. The WHO reports 250,000 to 500,000 deaths annually due to the flu, the majority due to pulmonary and cardiovascular complications. An annual economic burden of over $25 Billion USD is associated with the flu in the US alone. It is therefore a high priority target for primary prevention by national health organizations.
The Flu Pandemic
The Influenza pandemic is becoming one of the major concerns among health authorities due to increasing international travel, as well as over-population associated with poor sanitary conditions for humans and livestock living together in some developing countries. As a result, there is a heightened risk for emergence of new and more violent and resistant influenza virus strains as well as increased human infection by animal virus strains, as observed since 1997 with the Avian Flu and more recently with the 2009 Swine Flu Pandemic.
2009 has seen a global outbreak of a new strain of influenza A virus subtype H1N1, which has already been reported in over 480,000 worldwide, with at least 6,071 deaths (as of 1 November 2009).
Indeed, the Avian Flu (H5N1) virus had previously raised concerns about a potential human pandemic because it is highly virulent; it is spread by migrating birds and can be transmitted from bird to human. A further change of this virus could potentially result in a human-to-human transmission of the disease and lead to a worldwide pandemic.
The Flu Vaccine
Despite the improvement in antiviral therapy during the last decade, vaccination is still the most effective method of prophylaxis. However, effective vaccines must be of the same type that is likely to be common in the following influenza season. Rapid changes in the viral surface antigens render the current strain-specific vaccines only partially effective. Commercial vaccines consist of whole, live-attenuated or killed virus or fragments of their envelope (surface proteins). Due to the ever changing nature of the influenza viruses, and the inability to predict the new strains to come, vaccine makers prepare the flu vaccine according to WHO expert’s recommendation, using three or four different strains every year (two influenza A and one or two influenza B strains). This “educated guess” process based on circulating strains from previous season is not always accurate, resulting in reduced efficacy of commercial vaccines. The average multi year effectivenes of the seasonal vaccine is estimated at 40% with significantly lower numbers in mismatch years. In the season of 2014/15 the effectiveness in the total popluation in the US was 19%.
A New Approach
New strategies for influenza vaccination include the development of vaccines based on short immunogenic peptides, called epitopes that elicit protective immunity.
The key factor for the success of this approach is the exact identification of those epitopes common to the vast majority of influenza strains and capable of eliciting a broad range and long lasting immune (both humoral and cellular) response.