Baum U, et al. - In view of the parallel use of injectable, trivalent inactivated influenza vaccines (IIV3) and a nasal spray, tetravalent live-attenuated influenza vaccine (LAIV4) in Finland from 2015/16 through 2017/18, researchers here sought to ascertain the relative protective efficacy of vaccination with each vaccine type against influenza among children under real-life conditions. They estimated vaccine effectiveness in 2-year-olds for all three seasons. They conducted a nationwide register-based cohort study in each season. In 2015/16, 2016/17 and 2017/18, 60,088 children, 60,860 children, and 60,345 children comprised the study populations. Outcomes suggest no clear superiority of either of the influenza vaccines in protecting children. The LAIV4 effectiveness was greater against type B vs type A and relative to the IIV3 effectiveness, greater effectiveness against type B was reported with LAIV4. To understand how influenza vaccines could be improved, analysis of vaccine effectiveness by vaccine and virus type is essential. Individual and programmatic decision-making processes require effectiveness estimates expressing also overall protection levels. Backed by this analysis, the vaccination program in Finland now endorses LAIV4 and injectable, tetravalent inactivated influenza vaccines replacing IIV3.