President Joe Biden, announcing that drugmaker Merck will help manufacture a vaccine developed by Johnson & Johnson, said the United States would have enough doses for every adult American by the end of May. That does not mean they would all be administered by then.President Joe Biden, announcing that drugmaker Merck will help manufacture a vaccine developed by Johnson & Johnson, said the United States would have enough doses for every adult American by the end of May. That does not mean they would all be administered by then.