The U.S. is awash in vaccine supply. Its new concern: Will demand keep up?

On the road to mass-vaccination, the U.S. is so far ahead that it's detecting new obstacles that remain, for much of the world, an afterthought on adistant horizon.

The proportion of the population who've received at least one dose is almost twice as high asin Canada, and it's 10 times higher for the fully vaccinated.

The vaccine supply in most states has ballooned tomore than one dose per adult that's allowedhalfof adults and nearly40 per cent ofthe total U.S. population to have receiveda shot.

Nowadays whenyou text friends to tell them a local clinic has doses available, it's increasingly common to hear the reply: No thanks, I've already got mine.

"It's pretty damn good," Paul Goepfert, a University of Alabama researcher who studies vaccines, said of the rollout so far.

So he's optimistic, right? Not quite.

In fact, Goepfert isworried that the U.S. might never cross that coveted threshold of herd immunity.

"I'm skeptical," he said of whether the country will reach herd immunity."At least not anytime soon."

Vaccine hesitancy ranks atop his causes for concern. The increasing abundance of U.S. supply is now shifting attention to thatother half of economics' most fundamental model: demand.

Whether enough Americans take the vaccine matters not only here but elsewhere, as the world pursues that ill-defined immunity threshold, which most estimates peg at about three-quarters of the population.

Blue states, red states

The rate of vaccinations is still increasing across the U.S. butthere's an emerging gap in how quickly different states areunloading supplies.And the gap is growing.

The states seeing the biggest daily increases in vaccinations are churning through their supply led by New Hampshire,which has now delivered at least one dose to 71per centof adults.

Other states have usedjust two-thirds of their supply and the daily increases are smaller: Mississippi and Alabama, for instance, have delivered at least one doseto 38 per cent of adults.

There's aneye-catchingpolitical trend developing.

Of the states with the most doses administered per adult, 14 of the top 15 voted for Joe Biden. As for states administering the fewest doses, 14 of 15 voted for Donald Trump.

Goepfert's own experiences attest to the trendlinein his state of Alabama.

Just weeks ago, he was being bombarded with requests from people who hoped that, through his work, he might help them score still-rare vaccines.

"I don'tget those calls anymore," he said.

Meanwhile, heworks at an HIV clinic and struggles to convince some patientsto take the vaccine, including people with serious pre-existing conditions.

He describes a spectrum ofvaccine hesitancy. Some skeptics can be convinced togetvaccinated, he says; othersflat-out refuse. Some say noout of fear;others have nofear of COVID-19.

One patient casually brushed offgetting vaccinated, Goepfertsaid, telling him: "I don't wear a mask. I haven't gotten sick. Why should I get a vaccine?"

Pharmacy slots unfilled

Vaccination appointments are going unfilled in certain places.

There were vacant vaccination slotsin dozens ofCVS pharmacy locations on Thursday in Tennessee, Mississippi, Louisiana, Alabama and Wyoming.

Yet the slots were all booked at its locations in Connecticut, Delaware, Massachusetts, New Hampshire and Minnesota.

One North Carolina county plans toshutits mass-vaccination siteafter this month because of droppingdemand.

After an initial rush, the site located in an old K-Mart is getting a fraction of its former use; a lengthy waiting list for vaccines has evaporated, and patients now have more places to get vaccines in Carteret County.

"I'm worried," said Ralph Merrill, an engineer who sits on the county board. Hiscounty has fully vaccinated one-quarter of its population, around the state average butfar from the eventual goal.

"I'd be surprised if we get much above 50 per cent."

He pauses and chuckles in mid-sentencewhen asked why he's worried: "There's a lot of people around here who I don't think they want to take the vaccine."

Like others, he describes vaccine hesitancy as coming in different varieties. At the Marine Corps base where he works, he said, some friends are cautiously skeptical; others offer wild conspiracy theories.

The Trump card

Trump won Carteret County, N.C., by 42 points.

Merrill is convinced politics is driving anti-vaccination sentiment, especially among people who generally distrust government.

The U.S. Congressanticipatedthat vaccine hesitancy might become a problem and set aside more than $1 billion inits newCOVID relief law for a public awareness campaign.

But Merrill seesa quicker, easierway to influence public opinion: get Trump to go on TV, talk about how his administration funded the development of vaccines, describe how he got vaccinated, and urge supporters todo the same.

"He's like the idol to a group of people," Merrill said. "That would be a good thing for him to do."

A wealth of polling data backs up the idea that vaccine hesitancy is highest among Republicans.

Three polls released this month put the number of Republicans who don't want a vaccine in the neighbourhood of 40 per cent that's roughly double the national average and multiple times higher than the ratio of anti-vaccine Biden supporters. Surveys also find higher-than average vaccine hesitancy among African Americans.

The tricky math on herd immunity

This is the kind of math that has Goepfert worried thatherd immunity might prove elusive.

Adults comprise 78 per cent of the U.S. population,and because vaccinations are mainly going to adults, he figuresthat nearly all adults will need antibodies from a vaccine or recent illness to get there.

He doesn't see how that could happenwith so many people hesitant to get vaccinated.

SomeU.S. states are now expanding the eligibility poolto include 16-year-olds.

The governor of Mississippi, Tate Reeves,recentlytried to convince some of the vaccineholdouts in his state by speakingforcefully about how he and his family have gotten vaccinatedand announcing newmobile vaccination clinics in priority areas.

"The next million shots are going to be harder to get than the last million. They're going be hard to get because of vaccine hesitancy," Reeves said at COVID-19 briefingin late March in which he announced that one million vaccine doses had been administered in the state.

"We've got to getcreative to get shots in arms. It was easy early on, in January, because we had a lot more demand than we had supply. We've always said that at some point, we're going to get to where there is as much, if not more, supplythan thereis demand. We're not there yet, but we're seeing the shiftvery, very quickly."

Politics: Correlation isn't causation

One infectious-disease expert and medical practitioner in the U.S. saidit's simplisticto attribute vaccine hesitancy entirely to politics.

Krutika Kuppalli, a doctor and researcher at the Medical University of South Carolina, said several factors shape your risk assessment, and it so happens these factors might correlate to political preference: the population density of your area, your education level, and whether you have regular access to health care.

She agreed vaccinationslots are filling more slowly in her area than before, and echoing other experts saidhesitancy comes in different forms.

Some issues are purelyclerical: people strugglingto navigate anappointment website, she said. More surprising are the stories that stem frommisinformation like one patient this week who expressed fear vaccines might worsen his unrelatedcondition.

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What's the long-term outlook

"The amount of the misinformation is unbelievable," she said.

"It astounds me how much is out there."

So what's next?

Kuppalli suspects vaccines for adolescents are part of any solution for getting to herd immunity, and even then it won't be easy.

She worries about new variants popping up in the manycountrieswhere vaccines remain rare, and saidit's unclear whether they will beeasier or harder to manage.

We might need occasional vaccine booster shots to protect ourselves, she said.

Goepfertalso suspects we'llbe getting booster shots, perhaps every couple of years.If things work out, he said, future variants will keep responding to vaccines, and COVID-19 might weaken into yet another form of the common cold.

That's his optimistic scenario.

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