States are delivering on President Joe Biden's promise that every adult in the country would be eligible to get the COVID-19 vaccine by Monday. Now health experts say the next hurdle is getting everyone to come out and get it.

Biden set the goal of full adult eligibility for April 19. With Hawaii, New Jersey, Massachusetts, Rhode Island and Vermont the last to expand access to the vaccine, all 50 states have now opened up the process to all adults.

That milestone comes as the Centers for Disease Control and Prevention says the U.S. has hit another goal: 50% of U.S. adults have gotten at least one dose of the vaccine.

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Despite the promising numbers, demand is dropping in a number of states. A recent Monmouth University poll shows about one in five adults say they're not willing to get vaccinated.

The divide is mostly along party lines, with 43% of Republicans who want to avoid the vaccine, 22% of independents and 5% of Democrats. The reasons vary from a push to maintain personal freedoms, to distrust because of past mistreatment of minorities by health professionals.

Other reasons include difficulty accessing shots, not liking needles or a lack of long-term safety data.

Health experts say whatever the reasons may be, it's all the reason to keep talking.

"Having that conversation in a way that doesn't make them feel judged or shamed by having like any kind of concerns or hesitations, and that allows them to at least feel a bit more comfortable with it," says infectious disease specialist Dr. Ruth Adekunkle.