A subset of white blood cells may determine who is best protected by seasonal flu vaccines.

Hideki Ueno at Baylor Research Institute in Dallas, Texas, and Octavio Ramilo at the Nationwide Children's Hospital in Columbus, Ohio, and their colleagues injected 49 adults and 19 children with flu vaccine. The researchers tracked cell types in individuals over time and discovered a particular class of immune cells that is activated on vaccination. These cells can boost production of existing antibodies that fight flu, but they do not induce production of new antibodies. This suggests that the current flu-vaccine strategy may be less effective in young children and against rare types of flu, such as H5N1.

Sci. Transl. Med. 5, 176ra32 (2013)