To the editor — In January 2018, PLOS ONE published the chemical synthesis of horsepox virus (HPXV) by a group of privately funded Canadian researchers. The authors state that “[s]ince HPXV may be extinct and the only specimen of HPXV that has been identified is unavailable for investigation, we explored whether HPXV could be obtained by large-scale gene synthesis.”1 The DNA sequence of the HPXV genome was published2 in 2006 and is publicly available in the US National Institutes of Health GenBank database. The Canadian researchers used the HPXV genome sequence as the digital template to ‘rematerialize’ the virus using DNA fragments ordered from a commercial provider in Germany. Viruses from the genus Orthopox have particular genetic structures (like terminal hairpin loops) that make them difficult to both sequence and reverse engineer, but the Canadian group overcame such technical difficulties using a helper virus, recreating a “faithful copy” of the HPXV template1.