Every adult 18 and older in the United States who received the single-shot Johnson & Johnson COVID-19 vaccine will be able to get a booster dose if the Food and Drug Administration (FDA) accepts a recommendation from its advisory panel. The panel unanimously voted Friday to advise the agency to authorize boosters for all adults, regardless of their health condition. As of Oct. 14, 15.2 million Americans have gotten the Johnson & Johnson (J&J) shot. Members of the Vaccines and Related Biological Products Advisory Committee heard from the FDA and Janssen, the subsidiary of J&J that developed the jab. Approximately 9,000 participants in J&J trials have gotten a second shot, though safety and effectiveness data was only submitted on a fraction of that number. Like Moderna and Pfizer officials, who successfully convinced panel members to endorse boosters, Janssen scientists tried conveying twin messages: their vaccine is holding up well against severe …