Vaccinations and antitoxins do exist for some biological agents. From the terrorist's point of view, probably the greatest barriers to the use of biological warfare agents are the unpredictability of the effect and the lag time between dissemination and the appearance of any significant results. There are other issues that may hinder the effectiveness or practicality of using biological agents for terrorism. The weather in the target area is very important in the use of aerosols, as higher wind speeds tend to break up the aerosol cloud. Stable wind direction is critical to a terrorist with a specific target in mind.
Optimum conditions occur more often during nighttime and early morning hours.
To date, even sophisticated terrorists have had a hard time making good on the threat of biological terrorism. The Aum Shinrikyo cult in Japan had more than a billion dollars in assets and 50,000 members, several of whom were skilled biologists. But the cult was unable to mount a successful biological attack despite numerous attempts. Instead, it used a nerve gas, Sarin, to kill people in an attack on the Toyko subway. Preplanning for an attack Until recently, terrorists have been satisfied to commit symbolic acts of terror rather than kill large numbers of people.