NEW YORK (AP) — The number of first-dose COVID-19 vaccinations is falling in the U.S., despite the spread of vaccine requirements across the country. And some experts worry that the move to dispense booster doses could undermine efforts to persuade the unvaccinated to get their shots in the first place. The average daily count of Americans getting their first dose is down more than 50% over the past six weeks. An estimated 70 million eligible Americans have yet to start vaccinations. Experts have long said the key to controlling the pandemic is inoculating the vast majority of the American public.