The CEO of Covid-19 vaccine maker Moderna warned earlier that the coronavirus that has brought world economies to a standstill and overwhelmed hospitals will be around “forever.” Public health officials and infectious disease experts have said there is a high likelihood that Covid-19 will become an endemic disease, meaning it will become present in communities at all times, though likely at lower levels than it is now.

Health officials will have to continuously watch for new variants of the virus, so scientists can produce vaccines to fight them, he said. Researchers in Ohio said Wednesday they’ve discovered two new variants likely originating in the U.S.

U.S. officials are trying to get ahold of more vaccines, but it will likely take months before the U.S. can vaccinate enough people to achieve herd immunity, meaning the virus won’t have enough new hosts to spread. Still, the U.S. will be one of the first large countries to achieve “sufficient protection” against the virus.