Johnson & Johnson said Thursday that U.S. regulators extended the expiration date on millions of doses of its COVID-19 vaccine by six weeks. The company said a Food and Drug Administration review concluded the shots remain safe and effective for at least 4 1/2 months. In February, the FDA originally authorised J&J's vaccine for up to three months when stored at normal refrigeration levels. Thursday's announcement comes after state officials warned that many doses in storage would expire before the end of the month. Vaccine expiration dates are based on information from drugmakers on how long the shots stay at the right strength. J&J said the FDA added six weeks based on data from ongoing studies assessing the vaccine's stability. The FDA has been reviewing expiration dates on all three U.S. authorised vaccines as companies have continued to test batches in the months since the shots first rolled out. The vaccines from Pfizer and Moderna, authorized in December, have a...