Vaccine development company Novavax on Monday announced it has expanded its Phase 3 clinical trial for its COVID-19 vaccine to children between the ages of 12 and 17. The company said it's testing its COVID-19 vaccine — NVX-CoV2373 — on some 3,000 pediatric patients across 75 U.S. locations. The company is testing two doses of its vaccine candidate spaced 21 days apart.