Johnson & Johnson's one-dose shot could be vital to vaccinating the rest of the country. But has it missed a critical moment?

Amid a months-long decline in daily vaccinations across the U.S., pitfalls in the rollout of Johnson & Johnson's one-dose vaccine have resulted in millions of unused doses, public skepticism and a diminished role in the nation's vaccine rollout. 

Johnson & Johnson had aimed to deliver 100 million doses of vaccine to states by the end of May, but fewer than 22 million have been shipped to states so far, according to data from the CDC. The shot currently makes up less than 4% of doses administered nationwide.   In Washington state, the lack of supply has diminished plans to target harder-to-reach communities with the shot and incorporate the vaccine in the state's larger rollout, said Dr. Umair Shah, the state's Secretary of Health.