A suite of News Features, Comment pieces and research papers in this issue focuses on vaccines and vaccination. In a Perspective , Rino Rappuoli and Alan Aderem present a vision for 2020, by which time rationally designed vaccines should be capable of tackling the triple problem of HIV/AIDS, malaria and tuberculosis. In Comment, Julie Leask asks how a greater acceptance of vaccination can be achieved in developed societies (page 443), and Heidi Larson and Isaac Ghinai outline the lessons to be learned from the long battle against polio in the developing world (page 446). In News Features, Roberta Kwok examines recent vaccine safety problems (page 436) and Corie Lok profiles immunologist Bruce Walker and his attempts to overhaul the field of HIV vaccines (page 439). Cover illustration: Serge Bloch.

The Canadian Arctic Archipelago contains one-third of the global volume of land ice outside the ice sheets, but its contribution to sea-level change is largely unknown. Gardner et al. use three independent techniques to reveal that mass loss from the archipelago was 92 ±12 gigatonnes per year in 2007–09, about three times greater than in 2004–06, and coincident with warmer summer temperatures. The record is too short to allow a firm conclusion on longer-term trends, but it is clear that the Canadian Arctic Archipelago is a significant contributor to sea-level rise. On the cover, an englacial melt channel within the Devon Island ice cap. Photo credit: Angus Duncan.

Control theory can be used to steer engineered and natural systems towards a desired state, but a framework to control complex self-organized systems is lacking. Can such networks be controlled? Albert-László Barabási and colleagues tackle this question and arrive at precise mathematical answers that amount to 'yes, up to a point'. They develop analytical tools to study the controllability of an arbitrary complex directed network using both model and real systems, ranging from regulatory, neural and metabolic pathways in living organisms to food webs, cell-phone movements and social interactions. They identify the minimum set of driver nodes whose time-dependent control can guide the system's entire dynamics. Surprisingly, these are not usually located at the network hubs. On the cover, part of the cactus structure, a subset of nodes that have a key role in the control of real networks, with nodes in blue and drivers in red, visualized by Mauro Martino ( go.nature.com/wd9Ek2).

When is a wing not a wing? When it’s a helmet. Insect wings vary enormously in size and shape, but all have one thing in common — they grow out of the second and third of the three segments of the thorax. Or do they? Prud'homme and colleagues have been looking at the treehoppers, close relatives of cicadas that have a bizarre and varied structure called the 'helmet' growing from the wingless first thoracic segment. The helmet is classically described as a cuticular expansion of the first thoracic segment. Closer examination shows that, in evolutionary terms, it corresponds to a third pair of wings. A striking feature of body plans is their relative stability over long evolutionary times. The discovery of this previously unknown variation of the blueprint for insects illustrates how a structure relieved of its original role is free to evolve new functions and morphologies. On the cover, the treehopper Hemikyptha marginata. Cover image: Nicolas Gompel.