Donald Trump's pick for head of Health and Human Services is trying to walk back his anti-vaxxer past — but still sowing doubt for the life-saving public health measure

Pfizer's stock dropped 4.3 percent while Moderna's fell 3.1 percent and Novavax saw a 2.8 percent dip in its stock Friday morning.

Vaccine stocks have struggled since RFK Jr.'s appointment to health secretary, with Moderna and Pfizer seeing the deepest losses.