Mark Lennihan / POOL / AFP Uncovering and explaining how our digital world is changing — and changing us. On Monday morning, the first person in the United States received a dose of the Pfizer/BioNTech Covid-19 vaccine. Now images of Sandra Lindsay, a nurse at Long Island Jewish Medical Center in Queens, are going viral. But over the coming weeks and months, she’ll be far from the only person showing up in social media feeds getting inoculated. At the dawn of the pandemic, celebrities and influencers flooded our feeds with content urging us to take preventive measures, like hand-washing, social distancing, and mask-wearing. That wasn’t a coincidence: Public health leaders and campaigns strategically encouraged and recruited those with large online followings to use their platforms for good.