Until recently, seasonal influenza vaccines were designed to protect against three different influenza viruses, and so were referred to as trivalent influenza vaccines. The seasonal trivalent influenza vaccine protects against two influenza A viruses and one influenza B virus. However, there are two different types of influenza B viruses that can circulate in a given influenza season and the recently introduced quadrivalent vaccine provides protection against both types of influenza B. The quadrivalent vaccine therefore offers broader protection against the influenza B viruses that may circulate.
How well will the quadrivalent influenza vaccine protect against influenza?
Influenza immunization builds up antibodies against the influenza viruses in the vaccine, making it easier to fight influenza infection before it starts. The quadrivalent influenza vaccines offers broader protection than the trivalent influenza vaccine since it contains four strains of influenza virus, two influenza A strains and two influenza B strains. The TIVs and quadrivalent influenza vaccines provide the same degree of protection against the three strains they share in common. Generally influenza vaccines offer about 60% protection when the vaccine and circulating strains are well matched. The quadrivalent influenza vaccines will offer extra protection if the additional B strain in that vaccine is in circulation during influenza season. It takes about two weeks following immunization to develop protection against influenza; protection can last up to one year.
Click here for more info: https://www.cdc.gov/flu/protect/vaccine/quadrivalent.htm