mRNA vaccines are the best way to avoid ADE (antibody dependant enhancement) and to ensure that original antigenic sin won't be such an issue. Since the antibodies produced from the mRNA vaccines are highly neutralizing the risk of ADE is extremely small. Since the S-protein is highly conserved the risk of modifications of this protein are small and therefore original antigenic sin risk is also small. Having produced antibodies from the "live" virus itself you are at risk that your antibodies will not be nearly as effective with other strains since your antibody targets could be for other proteins found on the capsid that are not highly conserved structures and any other serotypes are more likely to not be neutralized by them, thereby leading to ADE (even though ADE in sars-cov-2 was not found to be a problem in rhesus monkeys and humans). This is the reason that the second infection of Dengue can be so deadly since a different serotype of Dengue is able to use antibodies to circumvent the immune system leading to hemorrhagic fever (also why an effective vaccine for dengue has not been made). Now I see the possibility that the immune system forgets the current antibodies to actually be a blessing. This would hopefully mean that the risk of Original antigenic sin would be circumvented and that as new strains are found new vaccines specific to that serotype are effective at generating highly neutralizing antibodies.