Yang Y, et al. – In a few countries, a recombinant, live–attenuated, tetravalent dengue vaccine (CYD–TDV) was licensed for children of 9 years old or older, in this work, researchers determined the dependence of this vaccine efficacy on baseline immunity status and age groups. They identified the CYD–TDV vaccine as highly efficacious for all dengue serotypes among children older than 5 years who have acquired baseline immunity from previous exposure. No explanation on the basis of increasing prevalence of baseline immunity with age could be made for increasing vaccine efficacy with age.