Invivac® is a virosomal sub-unit vaccine. The combination of a liposome and sub-units of the influenza virus is called virosome.
Liposomes are small empty spheres consisting of a lipid bilayer membrane.

The viral antigens hemagglutinin and neuraminidase are anchored into this lipid bilayer, thus mimicking a natural influenza virus particle. The virosomal sub-unit influenza vaccine Invivac® has been on the market since October 2004.