The Biden administration is expected to begin the process of expanding the booster authorization to all adults as early as this week, according to a source familiar with internal planning.Why it matters: America's booster campaign got off to an underwhelming start, potentially leaving millions of vulnerable people at risk as the holidays approach.The big picture: The pandemic still isn't over, and the data is clear that vaccine effectiveness has waned over time and with the rise of Delta — but also that a booster dose restores protection against the virus to remarkable levels.Despite disagreement among experts about who needs a...