>correlation is not causation<
I know this, I used the word correlation purposefully.
Australia and HI didn't sustain CCD in 2006-2010.
I did not say that varroa couldn't be a contributing factor.  What I said was not all CCD colonies were being over-run by varroa mites.  Some were, many showed no visible sign nor molecular signs (varroa proteins). of varroa.  Those with varroa were obvious, as was often the absence of strips or any effort to control varroa.
After the December and January collapses of 2006-2007, by February, some beekeepers had 2, 3, or more 'treatments' for mites in their hives, desperately trying to cure CCD.  For national news stories, I had to police yards the day before to remove illegal chemicals and multiple strips.
I will not argue that varroa isn't probably the biggest issue facing beekeepers worldwide.  
My point was - over the hundreds of beekeeping businesses and locations that I observed fand sampled from 2006 through 2010, we saw every type of beekeeping from those with great looking equipment, rigorous management plans, to the complete lack of any real management, and yes, even some PPB that didn't need anything else to kill their bees.  What we did not see was any difference in the effects, scale of effects, etc. that correlated  with either PPB or Best Management Practices as having any perceivable effect on whether the beekeeper's colonies collapsed.  CCD was an equal opportunity syndrome. PPB obviously didn't help, but BMP didn't protect.  Conversely, I saw yards with severe, untreated varroa, PPB to the extreme, that were not failing, exhibiting CCD.
The data showed only two correlative factors that were consistent in all of our hundreds of analyzed samples from CCD colonies - Nosema ceranae and one or more viruses.
As per external factors, weather appeared to be a part of the issue in CA.  When going to inspect and sample a reported CCD location, if it was in low lands, near water, with early morning fog, it was likely to be showing the established signs of CCD.
If on a sunny, hilly, breezing area, it often did not have CCD, although it might have had another problem.
Again, in that first year, a MT Beekeeper dropped 4 semi-loads in CA.  Two in lowlands, two on hillsides.  All of the bees came from his yards in MT, all were delivered within a few days of each other.  All of the lowland loads began to collapse with a couple of weeks, none of the upland ones did.  Same bees from same source location, same owner, same management practices.
I was conducting bee research studies in various parts of the USA before, during, and after first tracheal mites, and then varroa mites appeared in the USA.   Even they changed over a period of time - tracheal was a big problem for a short time, now is patchy, doesn't seem to be an issue.  Varroa, if anything, seems have gotten worse, although my bias is that's more of a beekeeper thing than a mite thing.  Overuse of treatments though is a factor.  Not monitoring and taking steps to control varroa appears to be a bigger issue with the explosion of new beekeepers since CCD, and the internet promoting natural and no treat beekeeping - things nice to aspire to, but not so easy to do successfully.  The problem, which we address in our classes, one needs a plan for what to do when natural or no treatment fails.
What that plan is not is buying bees, throwing them in a box, feeding to encourage swarming - all of  which is a sure fire way to spread bee pests and diseases.
Varroa appears to be the biggest single problem worldwide.  As our knowledge of viruses and tools to detect bee viruses increases, we're learning, bees aren't that much difference than humans.  Your COVID analogy is apt.  We have probably been under-estimating the effects of viruses since we've only recently have been able to detect them and the multiple strains of specific viruses.  It's like the studies that say Nosema ceranae didn't induce measurable harm - which I'd argue, may be true if you don't also have one or more viruses that may trigger the tipping point.
But attributing all bee losses and especially CCD to mites alone is not supported by the data.  It is a good excuse for explaining away bee losses - again, everyone knows varroa is a serious problem, so if you are a commercial beekeeper who loses 50% or more of their colonies in a single season, better to claim loss to varroa than to CCD.  Growers are likely to commiserate, tell you to get back to them when you've gotten your varroa problem under control.  They're more likely to look for other bee suppliers if you claim the boogey man CCD.  That has been in the public memory as something akin to a bee version of anthrax.



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