Nat. Med. 15, 293–299 (2009); published online 15 February 2009; corrected after print 6 April 2009

In the version of this article initially published, a “left” and “right” designation was switched in the legend for Figure 4d. The legend should read “FCICA of peripheral blood CD8+ T cells from the four protected vaccinees, examining the response of these cells to SIV proteins that were (Rev-Tat-Nef) or were not (Pol and Vif) expressed by the administered RhCMV vectors before (left) and 133 d after (right) initiation of the SIVmac239 intrarectal challenge protocol.” The error has been corrected in the HTML and PDF versions of the article.