The U.S. has surpassed President Biden's goal of administering 200 million coronavirus vaccine doses four months into its massive vaccination campaign, but experts say that was the easy part.
For months, supply has been so limited that states were restricting access to specific priority groups and many people who wanted a shot couldn't get one. But now every person over the age of 16 is eligible, and more than half the country's adult population has received at least one dose.
The nation is fast approaching the tipping point of vaccinations, where supply will outstrip demand. State and federal officials are going to need to find the best message and best method to get shots to the people who are either hesitant, unable or just indifferent.
Doing so will require a change in tactics, likely in how vaccines are distributed to states and how states allocate their doses to get the shots into as many people as possible.
"This will be much more of an intense ground game where we have to focus on smaller events, more tailored to address the needs and concerns of focused communities who have different sensitivities and different needs," said Steve Stack, commissioner of the Kentucky Department for Public Health.
Polls show vaccine hesitancy is declining, but the holdouts are not monolithic, and experts believe trusted messengers will be needed.
Some people are most worried about side effects, some are concerned about the safety of the vaccines and some people don't think COVID-19 is a problem at all.
"We have to do work there to make sure we're understanding their motivations and getting them answers to questions they may have," said Nirav Shah, director of the Maine Center for Disease Control and Prevention. "As we approach these groups, whether it's the not able, the not now or the not ever, we have to do so with an attitude and tone of respect."
According to a Kaiser Family Foundation analysis, the tipping point on vaccine enthusiasm could happen nationwide in as little as two to four weeks, though it's already being seen across some states, especially in the Southeast.
In Mississippi, for example, only about 22 percent of the population has been fully vaccinated, and in Alabama the number is around 20 percent, according to the Centers for Disease Control and Prevention.
If the drop in demand isn't addressed, the country may not be able to achieve the levels of protection needed to stop the spread of the coronavirus.
The concern is the areas that have the lowest vaccination rates could lead to more infections, and potentially more contagious variants.
States are already expanding hours at vaccination clinics and allowing more walk-ins. Public health staff will need to establish mobile clinics and go door to door in some communities.
A lack of demand has led to the closures of mass vaccination sites across several states, and officials said they will eventually need to shift and focus more on administering vaccines out of individual physicians' offices and community clinics.
The logistics of doing so are complicated, because it would require the Biden administration to work with manufacturers and ship vaccines in much smaller quantities, as mobile clinics and physician offices may only be able to vaccinate a few dozen people a day.
State officials said the federal government is aware of those concerns, and there are ongoing conversations about drug packing.
But there's currently too much risk of wasting doses. Until the numbers fall further and the packaging issues can be resolved, the demand overall still justifies using large sites to vaccinate thousands of people a day, said Marcus Plescia, chief medical officer of the Association of State and Territorial Health Officials.
"People who are highly motivated to get vaccinated, the mass vaccination clinics are perfect for them. They just want to get it done, and they want it as efficient as possible," Plescia said.
"But if you want to talk through it with somebody, then you really do have to find a setting where you can do that. ... That's not going to be in a mass vax clinic," Plescia said.
Jennifer Kates, a senior vice president at the Kaiser Family Foundation who co-authored the tipping point analysis, said while states shouldn't be closing mass vaccination sites yet, they also should already have invested in neighborhood sites and mobile clinics.
"Getting out to local communities with mobile vans, with door to door, that's going to take a lot of effort. There's going to be a point where some of that shift will happen," but it's not completely there yet, Kates said.
Some states have begun opening their mass vaccination sites to walk-ins, but it's often still limited to older populations.
In New York, for example, Gov. Andrew Cuomo (D) said that as of the end of this week, people 60 and older can get vaccinated at 16 state-run mass vaccination sites without an appointment.
In Washington, D.C., Mayor Muriel Bowser (D) opened specific walk-in sites across the city for people over 65.
States may also need to rethink how they distribute vaccines across different areas if some cities or even specific neighborhoods are seeing a downturn in demand.
"Just having the right number of vaccines in a state does not guarantee that you have the right number of vaccines in a local community that needs it, and you have to combine the demand generation with locating the supply in the right place," Kates said.
The Hill and Nathaniel Weixel contributed to this report.
Comments