A pandemic might be the method of killing most humans that requires the least intelligence, but killing a lot of humans may not be the takeover step that requires the least intelligence. It seems possible that an AI becomes capable of killing much of humanity but lacks the physical infrastructure to ensure its own survival (which is likely to be an instrumental goal for fulfilling whatever weird terminal goals it has).

I can imagine a scenario where the AI is smart enough to make a deadly virus but where that's the easy part. The hard part is getting enough capable robots integrated into things that you don't miss the humans. Right now, the humans are doing a lot of important tasks the AI wants, like keeping on the electric grid, mining the minerals that go into computer chips, building data centers and solar panels and rockets and scientific instruments, and servicing critical infrastructure. Making robotic systems that do those things and getting sufficient numbers of them built in the real world may be harder than making a virus, so an AI might be capable of creating a super virus but still spend years working on robotics advancements and self-improvement to achieve those advances, and by the time it has the automated economy it needs to survive, it's radically superintelligent and has a plethora of options. In that scenario, it wouldn't quickly jump to superintelligence, but rather the part where it kills the humans naturally comes at a point where it has relatively slowly become superintelligent.

There are ways the AI might try to use a virus before the existence of the automated economy as a control step rather than as a coup-de-grace (such as promising the humans a cure if they integrate it further, or using a targeted bioweapon to eliminate particular individuals who oppose its goals), and mitigation efforts could make those steps harder.

I think heightened pandemic prevention is generally a good thing, and in the AI context can mitigate some threats from malign human actors and non-superintelligent rogue systems (like versions of the swarms we've seen this year, but impulsively wielding bioweapons instead of cyber capabilities. We'll have to see if such things emerge; as capabilities increase they may get more strategic and less trigger-happy, and there may be less reward hacking related to deploying bio capabilities compared to computer hacking. My prediction would be that they'll deploy bioweapons far less freely than cyber intrusions for a number of reasons, but I don't know that "less frequently" will be equal to zero, and given the subject matter a single instance could be catastrophic). Pandemic prevention methods won't help you against a superintelligence any more than focusing on queen-checkmate-prevention methods will help you against stockfish, but they're helpful before that point.