WASHINGTON - Influential government advisers are deciding Thursday how best to expand the nation's COVID-19 booster campaign, including whether and when it's OK to "mix and match" brands for the extra dose.The advisers to the Centers for Disease Control and Prevention are slated to discuss who should get extra doses of the Moderna or Johnson & Johnson vaccines — and the bigger question of getting a different brand for the booster than people's original vaccination.The Food and Drug Administration authorized both steps Wednesday, as part of a federal push to broaden booster access for the U.S.