MEDI-559

MEDI-559 is a live attenuated intranasal vaccine candidate developed for the prevention of respiratory syncytial virus (RSV) infections, particularly in young children and infants. The vaccine was designed to stimulate an immune response against RSV by using a genetically engineered, temperature-sensitive strain of the virus that is attenuated to reduce pathogenicity. It contains several cold-passaged mutations and a deletion in the SH gene to confer attenuation and temperature sensitivity. Clinical studies demonstrated that MEDI-559 was immunogenic and biologically active in seronegative pediatric populations; however, there was an observed increase in medically attended lower respiratory tract illnesses among vaccine recipients compared to placebo. Due to these safety concerns and genetic instability issues with its attenuating mutations, development for RSV prevention has been discontinued[1][2][3][4][6].