Vaccinia (107 PFU) was diluted in heat-inactivated human plasma and mixed with varying concentrations of Povidone-iodine ointment (PIO) for 60 minutes prior to determining infectious virus levels by plaque assay (1A). Shorter incubation times were tested (1B) using 10% PIO, which effectively inactivates vaccinia within 5 minutes. The efficiency of inactivating virus directly on the vaccination site were tested by taking swabs from the treatment group on day 7, before and 1–2 hours after application of PIO (1C). Of 15 subjects with pre-existing virus titers, only 1/15 had detectable virus after PIO administration, resulting in a significant decline in the potential to shed infectious virus (P < 0.001; binomial calculation).
*In this sample, the swabbing procedure unroofed the eschar, exposing infectious virus that may not have been in contact with PIO. Dashed lines indicate the limit of detection.