News ‘Game changer’ single-dose vaccine from Johnson & Johnson is safe and 66% effective, company says January 29, 2021 Karen Weintraub, USA TODAY Comments Off on ‘Game changer’ single-dose vaccine from Johnson & Johnson is safe and 66% effective, company says The one-dose COVID-19 vaccine from J&J is a game changer because of easier and cheaper distribution. A large study has found it safe and effective.