For instance, let's take a look at Biogen (BIIB). Last week, the stock was up 46% on a single day (from 246$ to 360$) on optimistic news about some Alzheimer treatment. Today, the stock is down 30% because the drug may not be that effective. It's not the first time I've seen that, for a pharma stock. It's a frequent thing.
Today, Pfizer (PFE) announces a vaccine that would be effective by 90%. So, when the market opened, the stock was up 8%. It's not amazing but it's a good performance for such a giga cap (220B$ market cap). However, over the last 5 years, PFE is up by only 20% (including today's performance which helped a lot). And 20 years ago, the stock was more expensive than today.
Of course, there are plenty of exceptions to these two examples. But I've had my share of pharma stocks in the past and I think that this industry is a bit too hard. And while pharmas are way easier than financials to understand and analyze, I'm not sure that, on the ethical level, they're much better.
Maybe that Pfizer will do well with their vaccine. Actually, I think chances are high that Pfizer will go up substantially from here, because their announcment about a 90% effectivness sets the bar high and the company will be badly punished if the bar that they set themselves is not reached. In other words, it would be very stupid for them to prepare their own fall. But, who knows, the stock market is full of bad companies and stupid managers.