We only had to Footvax once, did it in in April - moved them onto clean grazing, checked the feet after 16 days and moved them onto new clean grazing, haven't seen footrot for 7 years (run a virtually closed flock). I used a separate, sterilised needle for each sheep, did them dry and have a good vaccination technique (according to my vet) but we found some of the tegs - maybe because they were thinner skinned, with less subcutaneous fat - had big lumps after a couple of days, which they then tried to rub on fenceposts and branches, so we had to gather them every couple of days for about three weeks and spray the sores with a/b spray to keep the flies away. If I ever needed to do it again I'd wait until the end of the fly season. The vaccine is too thick!