For many years, flu vaccines have contained three strains of influenza virus, two type A strains and one type B strain (TIV vaccine). Every year, the circulating strains vary, and scientists have to predict a year in advance which strains are most likely and companies have to start production of the vaccine long before flu season actually starts. Some years, the vaccine is a better match than others for what strains actually cause flu that year.
In this study, which was funded by a company that makes flu vaccines (GlaxoSmithKline), researchers evaluated a quadrivalent (QIV) flu vaccine that includes two type B strains. It was a multinational, randomized, blinded trial of the effectiveness of the vaccine.
The study did not compare the new vaccine with the existing trivalent vaccine; it only evaluated effectiveness at preventing flu infection in children 3-8 years of age. The vaccine had an overall effectiveness of 55%, and was 70% effective at preventing severe disease, which is similar to other studies of TIV.
This study is also helpful because few studies in the past have at effectiveness of vaccine in children (see Cochrane Review from 2012). The study is limited because it only looked at one season, and the strains change every year. Type B strains are usually less common than type A, but recently more strains have been circulating each year, and there has been more of a mismatch between vaccine and disease strains. It is unclear if quadrivalent vaccines will be any more benefit than trivalent vaccine. It is also possible that quadrivalent vaccines will have increased side effects from the increased antigen level.
A quadrivalent flu vaccine was released this year in addition to the trivalent, by a different company; however, it was released too late for most of us to use it, long after we had to place orders for the year.
