Commentary As the United States feverishly rolls out COVID-19 vaccination “booster” shots, Israel is reporting trudging toward a fourth shot in response to evidence of waning immunity protection and rapidly increasing cases after its widespread administration of a third shot last fall. Notably, all of these shots continue to use the original, long-extinct wild-type variant contained in the first generation of vaccines. This repeated administration of vaccines raises a risk of effects known as original antigenic sin (OAS) and antigenic seniority that, aside from a few exceptions, public health officials have not addressed. But before widespread boosters are administered, especially for younger people, it’s essential that doubts about this phenomenon be resolved. The concern is especially urgent because, as will be seen, there are already alarming signals that OAS and antigenic seniority might already be operative with respect to the rapidly spreading Omicron variant. Although the data are rapidly emerging …