Why was quadrivalent flu vaccine developed?

For years, flu vaccines were designed to protect against three different flu viruses (trivalent). Trivalent vaccines include an influenza A (H1N1) virus, an influenza A (H3N2) virus and one influenza B virus. Experts had to choose one B virus, even though there are two different lineages of B viruses that both circulate during most seasons. This meant the vaccine did not protect against the group of B viruses not included in the vaccine. Adding another B virus to the vaccine aims to give broader protection against circulating flu viruses.

Case in India

• More than 115,000 cases of influenza and more than 8,000 deaths due to influenza have been recorded since 2010, according to the ministry of health’s Integrated Disease Surveillance Project (IDSP).
• However, this number is limited to influenza caused due to one strain, H1N1, only. 
• The experts also noted that in 2017, the H3N2 and B subtypes of influenza virus were circulating, due to a build-up of the susceptible population.
• It was the first time the team had documented circulation of H3N2 and Influenza B.