The new boosters are supposed to be more effective at preventing infection, as well as preventing serious illness. Via the New York Times:

WASHINGTON — The Biden administration now expects to begin a Covid-19 booster campaign with retooled vaccines in September because Pfizer and Moderna have promised that they can deliver doses by then, according to people familiar with the deliberations.

With updated formulations apparently close at hand, federal officials have decided against expanding eligibility for second boosters of the existing vaccines this summer. The new versions are expected to perform better against the now-dominant Omicron subvariant BA.5, although the data available so far is still preliminary.

At this point, only Americans over 50 and those over 12 with certain immune deficiencies have been eligible for second booster doses. Although some federal officials pressed to bolster the protection of younger Americans now, officials agreed on the goal of strengthening everyone’s immunity in the fall with what is hoped to be a more effective booster, ahead of a possible winter surge of the virus.