Because of this, different types of vaccines are needed for different types of viruses. There are 4 main types of vaccines- live-attenuated, inactivated, toxoid, and finally SRPC, which stands for subunit, recombinant, polysaccharide, and conjugate. Traditionally to create a Flu vaccine, scientists take samples of the most common types of Flu virus being circulated during the previous year- usually 3-4 types (quadrivalent and trivalent flu vaccines). The H protein in Flu virus (the H part of H1N1) contains a head and a stem. Seasonal Flu vaccine will target the head of H which can mutate readily- again why new vaccines need created regularly.