Influenza, often referred to as 'the flu', is a respiratory infection caused by the influenza family of viruses. Infections with influenza are usually more severe than those with other respiratory viruses and involve a combination of respiratory (cough, sore throat) and constitutional (fever, headache, muscle aches) symptoms. In older adults and people with a range of pre-existing medical conditions, influenza infections can lead to serious and even life threatening complications.
Influenza is transmitted by moisture droplets from the respiratory tract of infected people by coughing, sneezing or speaking. When these are breathed in by a susceptible person the viruses they contain can enter the cells of the respiratory tract and multiply. The person will usually become ill within 2-3 days; however, it is not unusual for them to start shedding virus for up to a day before symptoms are noticed.
Two types of influenza viruses are of public health concern; they are designated as Type A and Type B. The surfaces of influenza viruses are covered with two types of proteins are continually changing by mutation to produce new strains of the virus, a process referred to as 'antigenic drift'.
As the circulating viruses change by mutation the antibodies produced by individual to fight previous infections become less effective at neutralizing the virus and within a relatively short time they are no long protective. Therefore infections can occur repeatedly throughout life and protection by vaccination requires annual dosing with updated vaccines. When a new subtype of influenza A occurs the whole population is highly susceptible and infection rapidly spreads worldwide producing a pandemic.
According to the World Health Organisation in annual influenza epidemics 5-15% of the population are affected with upper respiratory tract infections, resulting in hospitalization and deaths in high-risk groups. These annual epidemics are thought to result in between 3-5 million cases of severe illness and between 250,000 and 500,000 deaths every year around the world. Most deaths currently associated with influenza in industrialized countries occur among the elderly over 65 years of age.
The CDC in the USA estimate that 10% to 20% of U.S. residents get the flu each year, of which an average of 114,000 people are hospitalized for flu-related complications and 36,000 die each year from complications of flu.
A study of patients from 4 long-term care facilities in the US, completed by Carroll and colleagues, found that mean costs for the 1998-99 influenza season were between US$968 and US$1341 per case of influenza like infection (ILI). Between 18% and 27% of patients with ILI were hospitalized. The average cost of a hospitalization in our study was US$4,012. By contrast, in a study of 75 hospitals, Cox et al. estimated an average hospital cost of $10,108 for patients admitted from or discharged to skilled-nursing facilities. The Carroll study was completed from the payer's perspective and, consequently, defined hospital costs as the amount Medicare reimbursed as opposed to Cox who looked at the 'true' costs of care to the hospital.
In 1999 Dr Martin Meltzer and colleagues from the US CDC described a model of pandemic influenza and published their findings in Emerging Infectious Diseases in a paper entitled “The Economic Impact of Pandemic Influenza in the United States: Priorities for Intervention”. Their model predicted that the next influenza pandemic in the US may cause considerable impact in terms of loss of life, hospitalizations, outpatient visits and persons becoming ill but seeking no medical care. The mean estimated economic impact of an influenza pandemic will range from US$71 - US$166 billion with approximately 80% of the estimated loss due to loss of life.
In response to the significant burden of disease many developed nations recommend influenza vaccinations for high-risk groups. This includes all individuals aged 65 years or over, as well as those in long stay accommodation, with chronic respiratory disease, chronic heart disease, chronic renal disease, diabetes mellitus or suppressed immunity. The Advisory Committee on Immunisation Practices (ACIP) in the USA recommends vaccination for those aged 50 and over, and is also considering extending its recommendation to the vaccination of healthy children, particularly those aged up to 4 years. The increase in public awareness, vaccine availability and vaccination uptake rates amongst high-risk groups is causing growth in the influenza market. Powderject’s 2002 (June) annual report cites a 64% increase in sales of its flu vaccine Fluvirin, taking it to £66.7 million.
The market size for a new influenza vaccine is based on the price of currently available influenza vaccines (Fluvirin™ and Influvac™) and the number of individuals at high risk of contracting the infection. Guidelines published by the National Institute of Clinical Excellence (NICE) on the use of zanamivir (Relenza™) recommend influenza vaccination for all individuals aged 65 years or over, and also for individuals of any age living in long stay accommodation or with chronic respiratory disease, chronic heart disease, chronic renal disease, diabetes mellitus or immunosuppression. For the purposes of the calculation, it is assumed that the population over the age of 65 in developed nations is considered high-risk and will receive an influenza vaccination. This information is summarised in Table X.
X. Influenza vaccine market.
This is based on the current price per vaccination dose (approximately US$10 in the US) and the fact that routine immunisation is not recommended for children. It is possible however, that a new needle-free formulation could command a higher price. The estimate of market size for the over 65 age group of US$886 million, could increase to US$1.27 billion with the addition of the 0-4 age group, and increases again up to US$1.975 billion with the addition of children aged 5-14.