The US moved a step closer Wednesday to offering booster doses of Pfizer’s Covid-19 vaccine to senior citizens and others at high risk from the virus as the Food and Drug Administration signed off on the targeted use of extra shots.

The FDA authorized booster doses for Americans who are 65 and older, younger adults with underlying health conditions and those in jobs that put them at high risk for Covid-19. The ruling represents a drastically scaled back version of the Biden administration’s sweeping plan to give third doses to nearly all American adults to shore up their protection amid the spread of the highly contagious delta variant. However, more regulatory hurdles lie ahead before the dispensing of boosters can begin.