Feb. 20 (UPI) -- Regulatory predictability is crucial for vaccine makers as they plan trials for future products but shakeups in the United States' top health agencies are making the process more difficult to navigate. The U.S. Food and Drug Administration issued a refuse-to-file notice to drugmaker Moderna for its mRNA-1010 influenza vaccine earlier this month. The agency has since changed course , agreeing to review the vaccine, but the initial decision is just the latest signal to the