President Joe Biden and a top health official warned Monday that too many Americans are declaring virus victory too quickly, appealing for mask requirements and other restrictions to be maintained or restored to stave off a “fourth surge” of COVID-19. The head of the CDC said she had a feeling of “impending doom” if people keep easing off. The double dose of warnings came even as Biden laid out hopeful new steps to expand coronavirus vaccinations, with all adults to become eligible over the next 5 weeks.