At the beginning, it would be assumed that this is a VIRUS, a biological pathogen and would be treated like a plague.
The infection point of Japan is an island... once the effects are known (within an hour) there would be widespread TV broadcasts, and the area(s) of infection would be under quarantine.
Even if infected individuals are able to board airplanes, the news would be faster than travel. And in fact, the airplane would essentially be entirely infected with the possible exception of the pilots. Which would mean that those planes COULD be shot down to avoid spreading the plague anywhere else.
Essentially the 1 hour infection period to visible signs (and obvious change in behavior) is MUCH TOO FAST. Pathogens that are that quick are more likely to burn bright and fast and spreading quickly, but can easily be defeated by removing the source of the fuel. Think of a wildfire that runs into an area which no longer has fuel such as a parking log, freeway, ocean, etc. Unless the pathogen is able to hop the barrier, it will die quickly.
To make it work, you would really need two separate things...
- for the incubation period to be longer so that it avoids detection for longer
- an alternate deliver method other than the violent (and obvious) fangs
I would expect that nanobots would have some intelligence as well as a "desire" to survive. In fact, the network communication between multiple hosts could be considered some sort of hive intelligence. As part of the survival technique, while moving into a new area (including the initial infection point), the nanobots COULD slow down the incubation period.
For example, a bite might be able to inject 1000s (or millions) of nanobots into the new victim. But a spray of nanobots might also be able to infect people, even surviving on surfaces for days. Once a person picks up even a single nanobot, it might take much longer for that one nanobot to replicate enough duplicates to have the same effect as a single bite.
Also consider the effect of touch spreading the nanobots, especially before there are visible symptoms. An infected person touches the doorknob, spreading 100s of nanobots on the surface. Intelligently, only a single nanobot attaches itself to the next human to touch the knob... infecting 100s of people during the day.
Add to the weaknesses...
Communication wavelengths between hosts could be identified (radio signals?), and possibly jamming allowed. With enough sensors tuned, unaffected humans could be able to track infected individuals/groups.
Possible to render the nanobots inert in some way, such as an EMP?
Comparing Biological Pathogens to Nanobot...
Viruses seek to destroy and breed. Ultimately they exhibit self-destructive behavior when they so completely overwhelm the host. As they infect each cell, they rewrite the DNA of the host cell and use its own factories to replicate more of the virus... and once critical mass occurs, the cell explodes spreading the virus to other cells.
This nanobot infection has an entirely different approach... while it also wants to destroy (because that is their programming) and to breed, they do not NEED to. Once nanobots reach the levels of stability, they would not need to "feed" very often... only enough to sustain their energy requirements, which would be much less than replication requirements.
The nanobots do not require the cells... they only require the building block materials in the cells... which means they would destroy the cell walls first and break apart the components into useable building blocks for either energy or replication.
In addition, the nanobots do not ultimately seek to kill the host... they seek to remake the host into something their creators designed, and then sustain this new host in a symbiotic relationship INSTEAD of a predator relationship of biological viruses.
Conceivably, the nanobots could elect to augment their host and use the memories and abilities of the host to achieve their goals with greater results. For example, a host was previously a military general, and now the nanobot "network" has access to creative strategy and knowledge that is outside of the original programming. Certain behaviors couldn't be suppressed by the host... such as the craving for blood and to spread the plague, but after those needs are satisfied (fed) then other goals could be achieved.
The result is that humans actually have a highly intelligent foe that is far more devious than simply defeating a plague.