Here on AH the problem is folks don't have a good medical understanding of the medicine/biology behind these sorts of things. For example, pneumonic plague is the same as bubonic plague, just a different form (both caused by Yersinia Pestis). Because bioweapons can spread rather widely and uncontrollably, in most cases you need to make sure you have appropriate vaccinations and/or medications for your own forces/population before you deploy them. Note that this was not necessary for VEGETARIAN because anthrax is not transmitted human to human so as long as you avoid contaminated areas, eating contaminated food you are safe.
Aside from the issues of being relatively slow acting, the problem of uncontrolled spread is the biggest problem. Delivering biologicals (whether bacteria or viruses) by missile is a real problem. Between the problems of keeping most such agents viable in a warhead (which means you can't have them preloaded easily) and the issues of heating during the flight, there is the fact that any sort of bursting charge to spread them will end up destroying a significant percentage of the agent and dispersal may be minimal.
As a strategic weapon, whether against populations or food sources (livestock or crops) biological weapons can be used, however getting them where and when desired is difficult. Tactically they have limited value and are dangerous to your own forces. In theory, given current or near term technology, tailored viruses as possible. If you can find a genetic marker on cell walls or similar that is specific to your "enemy" you could make a virus that would only be effective against folks with that marker as long as your population does not have that marker.
For a country like the USA, where you have an increasingly genetically mixed population this is problematic for both you and your enemies. For enemies, you can't be sure about the desired marker will be on US troops/population you target. For the USA this means the "enemy" marker you use may be present in some of your population. A relatively homogeneous population, like Korea, China, Vietnam, or various African states would be most vulnerable to this sort of attack and therefore hopefully less likely to use them.
In short biological weapons are very scary and dangerous, but IMHO are only good as terror weapons against a population, and very limited in use tactically.