My bad. Jimbee. You are correct.
It's not a vaccine, it's something called variolation which uses puss from small pox victims. This site explains it far better than I can. It's somewhat off topic, but I think it's an interesting story in the fight to prevent various infectious diseases. Jenner carried variolation one step further using the much less dangerous cow pox to protect against the more lethal small pox. I guess that's when it became more like today's vaccination. It took a good 200 years of progress to eventually wipe small pox from the face of the Earth.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1200696/
Apparently, they did their version of group testing just as we do today. Though I dare say the idea of testing it on orphaned children would not be acceptable today.
Note: I looked in a mirror after writing this and can barely make out what might be left of my small pox vaccination scar.