Moderna and Pfizer are both pursuing possible versions of their doses adjusted for the B.1.351 variant first spotted in South Africa, though research so far suggests their current vaccines may remain mostly effective against the mutant. The AstraZeneca-Oxford vaccine, which isn't authorized for use in the U.S., has been found to provide only "minimal" protection against the South African variant. "The reason they are choosing that strain is it's one of the ones we know about now, with the variants of concern that are out there, that's the most antigenically different," said Mascola. Mascola also raised the possibility that developing a booster with the South Africa variant could provide more protection. "For example, if we boost with the B.1.351 strain and we see that the serum antibodies are broader, not only do they neutralize the original strain but also B.1.351 and other variants, then that may be a preferred approach," added Mascola.