When I say valid relative to long term effects, it is meant that long term effects have not been ruled out as has been typically done with every other vaccine produced. Unlike other vaccines which went thru 5 or more years of trials to rule out adverse effects, Covid is experimenting on people right now and cannot rule out long term adverse effects until it is trialed for a few more years.
So, nobody knows if this experiment is going to work long term. That's the gamble.