精选优质文档-倾情为你奉上Smallpox vaccinationsmallpox is caused by the variola virus and is most often transmitted by inhaling the virus.天花是由天花病毒引起的,通常是通过吸入病毒传播it has an incubation period of between 7 and 17 days,after which symptoms begin to appear.the inital symptoms are flu-like.A significant feature of the disease is the development of blisters on the upper part of the boby,which eventually scab over and leave scars when the scabs fall off. around 30 per cent of those infected with smallpox