[arkfreepdom]

No one knows for sure, but there is a good chance some immunity is conferred for a lifetime. Studies done many years ago suggest that people who had had cow pox were immune their entire life.

[dalereed]

I was vacinated as a child and 20 years later was given another vacination by US Customs when I returned from Mexico in 1958 and it didn't take therefore my first one was still effective after 20 years.