If today were an expiration Friday, you can see how the opening lesson can work.
Suppose you were long Moderna calls at 435 expiring today. At 4:00 pm they were worthless as the stock closed at 434.46. At about 4:40 pm, Moderna traded at 440 in after hours. A fast phone call to the broker would result in an in the money exercise.
The same can happen Friday depending upon the timing of and direction of the vote on PFE's booster.