I’m pretty sure that if you have the antibodies they don’t go away. The antibodies are markers for this specific virus. They simply tell the right “attack cells” where to go and what to attack. There were several reasons why the initial virus was so virulent, especially with the elderly (weakened immune systems due to age). For others it was because our antibodies didn’t recognize it…so one’s body was late reacting or it over reacted by throwing everything at the virus including the kitchen sink (causing severe swelling, especially in the respiratory system). The younger you are the stronger your immune system…this is why the virus has less of an effect on this demographic.
Bottom line: if you are in the high risk group, get the vaccine. If you’ve had the virus, you’re probably in the clear. If you haven’t had either, protect yourself.