(This is just a random chart showing an uptrend. The company is irrelevant to this illustration.)
Let's assume this chart shows 6 months of market movement. Where will this stock be in two years? Can you just extrapolate a line four times longer than it is continuing to go up?
No. It looks promising, but the long-term movement is just an educated guess, even by the smartest minds on Wall Street.
This is an analogy to the COVID vaccine. So far, it's promising, but we simply don't know with any real certainty what's going to happen in the long term. It might be even better than promised. It might be worse. We simply don't know.