Release a mild and less contagious version of the bioweapon in your own population a year or more in advance of the planned attack. This will inoculate your population and any other populations you want to protect. A mild and less contagious version of your bioweapon is used because: 1) a mild illness will not be noticed by adversaries, and 2) a less contagious virus will allow more accurate targeting.
Use covert agents to seed the virus in enough places to infect most of your population. Transport hubs, large schools and factories, market places, and so on can be clandestinely seeded with aerosolized virus as needed. A two-year schedule will allow enough time to inoculate your entire population without alerting your adversaries.
Once widespread immunity to the bioweapon has been established in your own population, the actual bioweapon can be released. The best place to do this is in your own country because this will provide plausible deniability. Several layers of excuses can be used to preserve plausible deniability. For example you can claim: 1) you don’t know how it started; 2) it’s a natural virus that came from animals; 3) someone else released it against you; 4) why would we harm our own people?
If this level of excuses begins to fail, you can release or encourage a layered story that: 1) it was released accidentally by a nearby research lab; 2) this is an even stronger story if the nearby research lab received funding from your target adversary or from world bodies such as the WHO. If other nations are entangled in the research and development of the viral bioweapon, they will avoid accusing you or at least delay their accusations for a long time. Time is your friend. As the months and years go by, people will become lost in a surfeit of details, many of which can be explained in several ways, thus increasing confusion and preventing clear conclusions.
Once the bio-attack has begun by first releasing the bioweapon in your own country, perform a psychological operation (psyop) that instills fear and panic in the world and an overwhelming requirement for governments to act decisively and quickly. This psyop may include dramatic videos of people dying in the street, videos of draconian lockdowns, of bio-suited workers spraying streets with something foggy, etc. At the same time, brag loudly that you alone are able to control the virus due to your superior form of government, thus goading other nations to follow. This technique will also play well at home.
The psychological and social confusion that ensues worldwide and especially among your adversaries is a major goal of your bio-attack. This is why a nasty virus that kills more people than in a normal year but not too many more is all that is needed; in fact, this is exactly the right kind of virus to use. The death toll will not be bad enough to start a shooting war and adversarial governments will make many mistakes in trying to control the virus.
A best case scenario is (some of) your adversaries decide to use your attack to their own advantage, which also happens to be your advantage as well. This might include removing a popular president, creating conditions that allow widespread election fraud, overturning economic concessions the previous president had forced on you, etc. Even better is lay the groundwork for this kind of outcome decades before the attack is launched and then use the many private relationships you have established and compromised to influence the behavior of your adversary’s government through think tanks, universities, research labs, medical institutions, mass media, social media, and so forth.
As you adversary overreacts and badly reacts to the virus, seed other parts of the world with the bioweapon thus causing worldwide fear and panic as infection rates and death rates spike in many places.