- The aim of the present study was to assess the post-smallpox vaccination complication rate in a cohort of Israel Defense Force recruits enlisted in the calendar years 1991 to 1996 and to compare it with rates reported, in similar age groups, in large surveys during the 1960s. The overall complication rate was 0.4 per 10,000 vaccinees, and the rate of severe complications was very low, similar to previously published data. We conclude that among young healthy adults, vaccination with smallpox vaccine is relatively safe and is associated with a low rate of complications. Severe complications were very rare in this age group in our study. However, the complication rate is increasing with the increased percentage of primary vaccinees.