Blood drawn from patients who received a single shot of Pfizer or AstraZeneca, a two-dose vaccine being administered in many countries but not the U.S., showed that one dose “barely inhibited variant delta,” the study found. The research showed similar results for those who produced natural antibodies after infection.
However, a second dose prevented infections in 88% of cases for the Pfizer vaccine and 60% for AstraZeneca, the study said.
It did not examine efficacy rates against the delta variant for the other vaccines being used in the U.S. — a two-shot vaccine made by Moderna and the single-dose vaccine produced by
Johnson & Johnson. The companies have said their vaccines provide strong protection against the variant.