Photo: Fiona Goodall/Getty Images WASHINGTON —States struggling to provide enough COVID-19 vaccines are likely just a few days away from a pivotal development in the vaccination race: the availability of a shot that requires only one dose. The game-changing Johnson & Johnson vaccine would differ from the two current shots by Pfizer and Moderna in several critical ways. By requiring just one dose, individuals won’t need to return several weeks later for an additional shot. That will be significant help in rural areas, and other places where residents are far from vaccination sites. It also has easier storage requirements than the current shots, which need extra-cold temperatures, and it can be kept in a standard refrigerator for at least three months