Governments refrain from biological warfare because it's not effective in achieving their aims, not because it's banned.
The Crusades, and then the Napoleonic invasion of Russia, were both notable departures, and both saw militaries surprised when their adversaries used tactics that had long been banned in Europe. The French were not expecting the Russians to put the torch to their own lands so as to deny the French forage. It made the difference that led to the famous infographic.
It's not unreasonable to think that nation-states refrain from biological warfare for moral reasons. As effective as they might be, the government using them wouldn't survive either due to politics or the hammer of the world coming down on them.
But by the time WW2 was over, society was conditioned to think of the technological aspects of the wars rather than the social. But chivalry used to be an actual thing.
Or if you're willing to plan ahead a little more... Develop the plague and the vaccine a decade or more before use, and spend the intervening decade adding it to childhood vaccines and seasonal flu shots. When it comes time for use, have the remainder of your population vaccinated.
I may be a pessimist, but I'd guess that "biological warfare is ineffective in achieving the aims of nation-states" won't be a thing forever.
At that point, I suspect aggressive deterrence will be the only viable option.
This still doesn't say good things about the survivability of the 3rd world, though. Even though modern server, desktop and handheld devices (let's call these "people with high-tier healthcare") are rather well hardened, older systems (people without that healthcare) and IoT devices (pets/farm animals/crops/nature) are notoriously vulnerable.
More likely, warfare biological or not is going to become even more rare and even less accepted.
If we keep up the forces that brought us peace, UN, EU, NATO, international trade, amongst many other forces, we're more likely to a world without war.
Viewed over the past 70 years, currents trends are merely a tiny bump. And indeed we don't see it catching on in the rest of the EU.
Note. We can't just hope for things to continue, but if we put in some work - odds are pretty firmly in our favor.
It's a weapon so dangerous to use that only the insane would even develop it in the first place.
There is no real way someone could set off a biological bomb and promise it won't make its way back to their own people. If it is infectious enough to wipe out the enemy completely, it is enough to spread to your home country. I think some of this is because a biological bomb would almost need to be something that can be carried through the air. There are probably some that could dust an area requiring direct contact, but if the folks have good hygeine, it'll be less of a threat. Contaminating drinking water is harder still - and again, you have to get through hygiene and all available filtration and sanitation systems that the enemy could be using.
You could infect animals, but animals being what they are they are likely to infect folks that aren't the enemy, including your own ground troops if you have any. Things that need direct contact with bodily fluids are even harder to use directly, and you are just as likely to kill slews of medical personell as you are the folks actually warring. Any accidents kill your own people first.
In any case, the outcome and international response will likely be similar to using nuclear warheads on a people. It might work, but you are going to kill lots of innocent people as well with something that keeps on killing long after the initial sickness due to the infectious nature of the thing.
Additionally, I highly doubt they'd mistake a biological for a traditional bomb: Any smart country with a scientific section would be looking at the components of bomb residue. If a biological agent is included, I think there is a chance of finding it and developing a cure before the kiling happened if it doesn't happen in a short timeframe.
Now, this is just for diseases. Poisons (biological or synthetic) and other sorts of chemical weapons are probably easier to control these things, and international response seems to be unfortunately slow on this depending on where in the world it is happening.
bioweapons and computer viruses are made to spread in a viral way, without the explicit intervention of humans. So once it's out there, it can't be stopped. In the future, nanobots could potentially be a third one too.
So yes, while biowarfare is banned, the consequences of doing it is far different.
They all spread memetically rather then biologically. In a way that is a bigger problem because it means effective eradication is virtually impossible, because even if the practice is eliminated, it has “spores” in human cultural record which are both difficult to eliminate and difficult (arguably impossible) to avoid adverse side effects when eliminating.
The same can't be said by bioweapons and AI.