Respiratory Syncytial Virus (RSV) is a paramyxovirus which has relatively little genetic variability and is present in only two major subtypes. Vaccine development has been a priority for over 50 years, but has met with little success so far. Especially an inactivated whole virus candidate has paradoxically increased mortality and disease severity, probably due to toxicity of immune complexes.
RSV has two major coat proteins (F and G). It has previously been demonstrated that virus entry is mediated by the F protein, which acts similar to influenza hemagglutinin. It has also been shown that neutralizing antibodies like pavilizumab bind to and stabilize the pre-fusion form of the F protein and thereby prevent membrane fusion with the target cell. Vaccine development based on soluble full pre-fusion F protein has been difficult due to its inherent instability.
In developing its vaccine candidate VVX005, Viravaxx identified peptide epitopes from the F protein which are responsible for RSV infectivity. They will be included into appropriate fusion proteins.
Clinical efficacy both for infant and elderly protection and possibly therapeutic vaccination in elderly patients will be studied, including evaluation of maternal vaccination of pregnant females in order to achieve placental transfer of maternal blocking antibodies and protection of the infant in the first six months of life, when the immune system is still immature.