"All of the low-hanging fruit has already been harvested. It's the tough customers that are left now," said Gretchen Chapman, a professor of social and decision sciences at Carnegie Mellon University.
Some companies have offered cash to workers who get the vaccine, but as the cost of treating COVID-1 cases skyrocket, businesses are hiking insurance premiums, a penalty for employees who choose to remain unvaccinated.
"There is reason to think that the fines will be more effective than the incentives," said Chapman. "There is this idea of loss aversion, that losses are weighed more heavily than gains, so a $200 incentive will not have as much influence as a $200 fine."
Delta Airlines' $200 monthly health insurance premium surcharge appears to be working. One-fifth of its unvaccinated workers got inoculated within two weeks of the policy announcement.
A new study from Affordable Health Insurance finds that 43% of unvaccinated employees say a premium surcharge would coax them into getting the vaccine. Another 25% responded that it might. Most said getting charged an extra $100 a month or so would probably seal the deal.
"Close to 68 percent of people earning over $125K per year were willing to get vaccinated to avoid the surcharge," said Dr. Noor Ali, a health insurance consultant with Affordable Health Insurance.
A recent analysis by the Kaiser Family Foundation estimates that last month the preventable costs of treating unvaccinated patients in hospitals totaled $3.7 billion, nearly twice as much as the estimates for June and July combined.
"Ultimately, at the core of it is really risk," said Ali. "You being an unvaccinated person are at risk at a higher and greater risk for contracting COVID, for being in the hospital."
Some say it's time for those who refuse to get vaccinated and end up in the hospital to shoulder those costs.
"If these facts and figures and numbers haven't convinced people, I don't think this additional surcharge is going to. I think, in fact, it might sway them just the other way, saying that this is an infringement on their individual liberties," said Ali.
With 150,000 new infections being reported a day, for some, the final decision could come down to personal wealth rather than personal health.