America’s vaccine campaign has collapsed from its previous highs. While at one point in mid-April more than three million people received the shot each day, now only around 1.2 million are – a rate that’s less than half of what it was at the peak.

So, the US might not make President Joe Biden’s goal to vaccinate 70 per cent of adults by July Fourth: At the current rates, roughly 175 million adults will get at least their first shots by Independence Day, falling short of the nearly 180 million needed.

If the vaccination campaign continues to stall out, it leaves the US vulnerable to a range of risks, from summer outbreaks in the South to continued resurgences of the coronavirus this fall to the possibility of new and dangerous variants.

While the vaccinated are protected, the virus is still spreading among the unvaccinated as quickly as it was during the massive outbreaks of the recent fall and winter.

That continued spread is particularly dangerous for those who can’t get vaccinated or don’t receive sufficient protection from the vaccines (if they’re immunocompromised).

So, it’s crucial to understand why a segment of the population, even a minority, isn’t getting vaccinated — as a first step to figuring out what will make a difference.

According to experts, there are a variety of reasons: lack of access to vaccines, a refusal to see Covid-19 as a threat, concern about the vaccines’ side effects, little trust in the vaccines or the institutions behind them, and belief in at least one of several different conspiracy theories.

Some of these reasons overlap and compound; for example, if someone doesn’t see Covid-19 as a big threat, they might decide the vaccine isn’t worth the side effects.

People in some of these categories might be persuadable while others might not. The most resistant are likely going to be really hard to move over at this point, staying at around 15 to 20 per cent of the population from poll to poll. But between these hard noes and the already vaccinated are a lot of people who have shown signs of movement before – enough to put a real dent in the fight against Covid-19.

So, understanding why people aren’t getting vaccinated and how to overcome those reasons is now crucial to beating back the coronavirus – to really put it in the past and guarantee it no longer threatens to warp all our lives once again.

According to the Kaiser Family Foundation’s surveys, about four per cent of Americans intend to get the vaccine as soon as possible but haven’t yet and another 12 per cent are in wait-and-see mode. Particularly among these segments of the population, access is still likely a major barrier.

It’s true that access to the vaccine has dramatically expanded in recent months, with the federal government now ordering and delivering far more doses than states actually use. A shot that once required an appointment potentially weeks in advance is now so abundant that it’s available to walk-ins at many pharmacies and other locales.

But there are still hurdles. People may not have the transportation to get to a pharmacy. A busy, inflexible family or work schedule may prevent them from taking time off work to get the shot and take a day or two off to recover from the possible side effects. Some people believe – incorrectly – that getting the vaccine isn’t free for everyone or just may not know that the vaccine is actually available to them.

“Access doesn’t just mean we’ve opened up eligibility to everyone,” Liz Hamel, director of public opinion and survey research at Kaiser, told me. “Access also means that I can find a way to get the vaccine without putting my livelihood at risk, or I can get it in a place I feel safe getting it.”

To combat this, vaccines could be deployed in more places, such as workplaces or entertainment venues. To reach a greater diversity of people, a study published by the National Bureau of Economic Research suggests offering vaccinations at Dollar General, finding that adding the stores to federal vaccine distribution programmes “would substantially decrease the distance to vaccine sites for low-income and minority US households.”

Employers could also offer paid time off for workers to get the shot and recover from any side effects — something the Biden administration has already subsidised. And public officials and agencies could do more to make it clear the vaccine is free for all and widely available for Americans 12 and older.

Even after the past year, some Americans still don’t see the coronavirus as a serious threat. Maybe they’re young, seeing that the virus isn’t as deadly for them as it is for older groups. They could be Republicans, who bought into former President Donald Trump’s claims that the coronavirus wasn’t a big deal and that Democrats, experts and journalists have exaggerated its risk. Polls show both groups tend to be less likely to want to get vaccinated.

Some also believe they don’t need the vaccine because they were previously infected with Covid-19 and have natural immunity to protect them, although some research indicates that the vaccines provide stronger immunity than infection.

Not seeing Covid-19 as a threat remains one of the biggest predictors for those who are most resistant to getting vaccinated – the hard noes. Many of them are the same people who spent much of the past year rejecting lockdowns and mask mandates as unnecessary and violations of their civil liberties.

“They are far more willing to believe that, basically, it’s okay. You’re fine. You’re not going to get the virus and so you can behave normally,” Kathy Francovich, a public opinion polling expert at YouGov, told me.

Unfortunately, these are also some of the same people for whom views about the vaccines seem most entrenched. Whether it’s a survey from Kaiser, YouGov, or Civics, around one in five Americans have consistently remained in this group over the past few months.

Still, there are possibly some ways to overcome this. Based on Kaiser’s polling, about a third of the hard noes would get vaccinated if it were required (by, say, an employer). Some would be persuaded by incentives, whether hard cash or free tickets for sporting events.

To put it another way, they may not be motivated by the risk of Covid-19 to get the shot, but some could get vaccinated if there’s another reason for them to do so.

• A Vox report