They note that the acellular vaccine does not offer as long-lasting protection as the old whole-cell versions did.
acellular a·cel·lu·lar (ā-sěl'yə-lər)
Containing no cells; not made of cells.
Devoid of cells; noncellular.
Of or relating to unicellular organisms that do not become multicellular and are complete within a single cell unit.