On January 25, President Biden extended Covid-related entry bans for travelers coming from the Schengen Area of Europe, Brazil, the Republic of Ireland, and the United Kingdom. Previously on January 18, then President Trump had declared these bans would end on January 26, but Biden revoked those orders with this new one. He has also added South Africa to the list. The bans for China and Iran are also still in place and have not changed.
Presumably, the National Interest Exception (NIE) for entry previously provided to F-1 students from the Schengen Area, Ireland and the United Kingdom, has not changed. For J-1 students and other select J-1 visa categories from these countries, NIE notations or letters from home country U.S. embassies would be needed to enter. It is not yet clear whether the NIE would apply to Brazil or South Africa. The U.S. Departments of State and Homeland Security may need to clarify in the coming days.