WASHINGTON - The government’s top infectious disease expert said Tuesday he is cautiously optimistic that there will be a COVID-19 vaccine by the end of the year or early 2021, and warned that the next few weeks will be critical to tamping down coronavirus hot spots around the country.Download the FOX 5 DC News App for Local Breaking News and WeatherWith coronavirus cases rising in about half the states and political polarization competing for attention with public health recommendations, Dr.