Varicella was troublesome when varicella vaccine (vOka) was licensed in the United States. Varicella's yearly death toll was ~100, indirect costs were massive, and varicella threatened immunocompromised children. Since licensure, varicella has almost disappeared; nevertheless, vOka attenuation has lacked a molecular explanation. Sadaoka et al. (T. Sadaoka, D. P. Depledge, L. Rajbhandari, J. Breuer, et al., mBio 13:e0186422, 2022, https://doi.org/10.1128/mbio.01864-22), however, have now identified 6 core single nucleotide polymorphisms (SNPs), which singly or in combination may contribute to VOka attenuation; moreover, they found a predominant variant allele of vOka encoding the viral glycoprotein gB that results in glutamine instead of arginine at amino acid 699. This change impairs fusion activity and the ability of varicella-zoster virus (VZV) to infect human neurons from axon terminals. Molecular virological studies of vOka are reassuring in suggesting that reversion to virulence is unlikely and should also help assuage current fears about VZV vaccination and alleviate unanticipated future problems. The impressive work of Sadaoka et al. thus represents an auspicious advance in knowledge.