Smaller markets are easily swayed by not so much money. Arbitrage is difficult because there is an inherent threat that you're betting against insider information.
In this specific case it's clear that the market doesn't represent our collective knowledge about hantavirus at all. Twenty days ago the odds of a hantavirus pandemic being declared by the WHO were ~10% and now it's 5%. This is just a reflection of the news cycle, it would be nuts to say that this is a reliable estimate for the underlying scientific facts.
That is not surprising. If your point is that 10% is not 5% and the odds change over time then you have unreasonable expectations. It's not an oracle. Where did I say it was? I said it's a quick and robust signal. Of course there's plenty of ways to get alpha, but those require both effort and domain expertise.
Is this a standard you hold to any other single signal? Name it. What signal (a) predicted <3% over a month ago and (b) you believed prior to be a reliable signal?
In this specific case it's clear that the market doesn't represent our collective knowledge about hantavirus at all. Twenty days ago the odds of a hantavirus pandemic being declared by the WHO were ~10% and now it's 5%. This is just a reflection of the news cycle, it would be nuts to say that this is a reliable estimate for the underlying scientific facts.