Although we believe it is likely that the current vaccines will continue to protect against severe disease caused by omicron, the possible need for a booster shot targeting a vaccine-resistant variant could be a reason to hold off for now on a booster targeting the original variant. For one thing, if omicron proves resistant to vaccine-induced protection against serious disease, then a booster dose with the current vaccine may not help. It’s also possible that repeatedly “training” the immune system to fight the original variant could reduce the effectiveness of a variant-specific booster. This phenomenon, called “original antigenic sin,” has been observed with influenza and human papillomavirus vaccines. In other words, for those not in immediate need of a boost, there may be a significant advantage to waiting until a booster more closely aligned with circulating variants becomes available; boosting on the original antigen could be counterproductive.
A trio of vaccine experts made the same point in https://www.washingtonpost.com/outlook/2021/11/29/booster-shots-universal-opinion/: