An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments and also achieves boiling-point elevation (anti-boil) to allow higher coolant temperature.
The strains of virus the trivalent vaccine protects against two A viruses (an H1N1 and an H3N2) and an influenza B virus. The quadrivalent vaccine adds another B virus to the vaccine which helps expand the level of protection to the recipient.
In the case of a pandemic, an additional vaccine may be created to protect against a particularly virulent or widespread strain of influenza. The need for a 2009 H1N1 influenza vaccine became apparent after the strains for the seasonal flu vaccine had already been selected, so that a separate vaccine was created. A quadrivalent inactivated influenza vaccine was licensed in the United States in 2012, and a quadrivalent live virus nasal spray vaccine was licensed in 2013. These formulations include two influenza B strains in addition to the A strains. This vaccines began to be available, along with trivalent vaccines, in the 2013-14 influenza season.