JULIE STEENHUYSEN and MICHAEL ERMAN  MODERNA Inc's experimental vaccine was 94.5% effective in preventing COVID-19 based on interim data from a late-stage trial, the company has announced, becoming the second U.S. drugmaker to report results that far exceed expectations. Together with Pfizer Inc's vaccine, which is also more than 90% effective, and pending more safety data and regulatory review, the United States could have two vaccines authorized for emergency use in December with as many as 60 million doses of vaccine available this year. Next year, the U.S. government could have access to more than 1 billion doses just from…