(NEXSTAR) – Gallup recently released startling results to a new poll.

When asked whether they would get the COVID-19 vaccine if it were free, 1.3 billion people said they wouldn’t. Only two out of three adults said they would get the vaccine — a percentage of the population too low to attain global herd immunity from the virus.

But there’s still hope that vaccine numbers will rise globally, and many U.S. states and businesses are incentivizing getting vaccinated with a series of ploys, ranging from free Krispy Kremes nationwide to a $1 million lottery in Ohio.

So what’s working to combat vaccine hesitancy nationwide?

Dr. Peter Chin-Hong, an infectious disease expert at the University of California at San Francisco School of Medicine, said it’s a combination of “the carrot and the stick.”

The carrot refers to things like the free Krispy Kremes. It’s about motivating people to get vaccinated using a positive incentive.

Some states are offering up cold-hard cash or bonds to the vaccinated, such as West Virginia, which is giving vaccinated residents a $100 savings bond.

Money, Chin-Hong says, has worked in other interventions, such as incentivizing people to get tested for drugs or sexually transmitted infections.

The other “carrot” is giving vaccinated people “soft benefits” in society, like the ability to jump in the mosh pit at a music festival or to attend a baseball game without getting COVID-tested beforehand.

“More liberties — I think that might encourage people to get it,” Chin-Hong said.

Then there are the sticks, or direct punishments for not getting vaccinated. These include employer and school requirements that say only the vaccinated can go back to work or enroll in classes.

There’s also the matter of immunity passports to travel. Some regions may, in the future, require visitors to show proof of vaccination before entering.

And of course there’s the biggest stick of all, which is getting sick with COVID-19 or spreading it to loved ones by not being vaccinated.