Novavax announced Thursday that its COVID-19 vaccine proved safe and effective in a study of 12- to 17-year-olds. … Its shots have been cleared for use in adults by regulators in Britain, Europe and elsewhere and by the WHO, and are under review by the FDA. Armed with the new data, Novavax plans to soon seek expanded use of its shots down to age 12. Later this year, it plans to begin testing in younger children.