The willingness to accept vaccination against both influenza A subtypes H5N1 and H1N1 among hospital based healthcare workers in Hong Kong was low Neither the change in WHO pandemic alert levels nor the experience of the SARS outbreak affected the potential acceptance of the vaccines Barriers identified include fear of side effects and doubts about the efficacy of the vaccines The strongest associations with the intention to accept vaccination were a history of seasonal influenza vaccination and perceived likelihood of being infected Evolutionarily Conserved Herpesviral Protein Interaction Networks Herpesviruses constitute a family of large DNA viruses widely spread in vertebrates and causing a variety of different diseases. They possess dsDNA genomes ranging from 120 to 240 kbp encoding between 70 to 170 open reading frames. We previously reported the protein interaction networks of two herpesviruses, varicella-zoster virus (VZV) and Kaposi's sarcoma-associated herpesvirus (KSHV). In this study, we systematically tested three additional herpesvirus species, herpes simplex virus 1 (HSV-1), murine cytomegalovirus and Epstein-Barr virus, for protein interactions in order to be able to perform a comparative analysis of all three herpesvirus subfamilies. We identified 735 interactions by genome-wide yeast-two-hybrid screens (Y2H), and, together with the interactomes of VZV and KSHV, included a total of 1,007 intraviral protein interactions in the analysis. Whereas a large number of interactions have not been reported previously, we were able to identify a core set of highly conserved protein interactions, like the interaction between HSV-1 UL33 with the nuclear egress proteins UL31/UL34. Interactions were conserved between orthologous proteins despite generally low sequence similarity, suggesting that function may be more conserved than sequence. By combining interactomes of different species we were able to systematically address the low coverage of the Y2H system and to extract biologically relevant interactions which were not evident from single species. Herpesviruses are subdivided into three taxonomic subfamilies (a, b and c) based on both genomic composition and biology according to a well-known phylogeny [1, 2, 3] (Figure 1A ). While all herpesviruses are structurally similar, the different subfamilies are highly divergent in genome size, content and organization. The genome size ranges from 120 kbp for varicella-zoster virus (VZV), which belongs to the a-herpesviruses, to 240 kbp for human cytomegalovirus (hCMV), a member of the b-herpesviruses [4, 5] . Gene-coding potential is reflected in the size of the genomes with VZV containing 70 open reading frames (ORFs) and hCMV containing ,170 ORFs. The overlap between the protein sets of the five viruses clearly supports the known phylogeny, but there are also some proteins shared among viruses not consistent with the phylogeny (Figure 2A ). Although the three subfamilies are thought to have diverged from a common ancestor around 400 million years ago (McGeoch 2006) , they still contain a set of 41 core orthologs present in all herpesviruses [6, 7] . Herpesviral core proteins are generally involved in fundamental aspects of viral morphogenesis (e.g. DNA replication, DNA packaging, structure and egress), and are consequently often essential for replication in cell culture [8, 9, 10] .