Only one product is currently available for the prophylaxis of respiratory syncytial virus infections and the need for a vaccine is high. The Phase I/IIa trial for MedImmune’s investigational vaccine MEDI-559 is therefore a big step in the right direction. However, the hurdles for this compound will only increase as it progresses in development.
MedImmune has initiated a Phase I/IIa clinical trial of its live attenuated intranasal vaccine (MEDI-559) in healthy children 1-12 months of age to help prevent severe respiratory syncytial virus (RSV) infections. MedImmune is also developing other live attenuated intranasal vaccines, such as MEDI-560 for the prevention of lower respiratory tract infections (LRTIs) caused by parainfluenza virus type 3 (PIV3) and MEDI-534 for the prevention of LRTIs in young infants that is caused by RSV and PIV3.
Although RSV usually only causes an upper respiratory tract infection similar to a common cold, it can also cause more serious LRTIs such as bronchiolitis that can result in hospitalization and sometimes death. Populations at higher risk for severe LRTI caused by RSV include the elderly, people with underlying disease, premature infants and children under four years of age.
The RSV market is currently dominated by another of MedImmune’s products, Synagis (palivizumab), a prophylactic monoclonal antibody. Synagis is the only commercially successful drug available for the prevention of RSV and reached sales of more than $1 billion in 2007 in the seven major markets (US, Japan, France, Germany, Italy, Spain and the UK). However, due to its high costs, Synagis is only prescribed to a very limited group, namely premature infants and children with chronic lung disease or congenital heart disease.
Despite the high need for an RSV treatment or vaccine, many large pharmaceutical companies have abandoned their efforts over the years, including Wyeth, Sanofi-Aventis, GlaxoSmithKline and Roche. In some cases, the problem has been financial: approved respiratory antivirals have struggled to meet sales expectations because of the relative cost of the product versus the typically mild illness suffered. However, the main reasons are more clinically oriented.
Aside from the major problem of diagnosing RSV and administering an antiviral product early enough to make a difference, developers face moral and ethical dilemmas in testing new drugs on infants and potentially premature babies. Furthermore, the respiratory syncytial virus itself has several characteristics that make the development of vaccines difficult. So although the progression of MEDI-559 to the next phase of development is a welcome advance, the vaccine is still some way from being available to those who need it.
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