The numbers of adults in the U.S. who have been vaccinated is holding steady, hitting a ceiling that could be disastrous if COVID-19 variants begin spreading. Approximately 67% of Americans have had at least one shot and 58% are fully vaccinated according to the Centers for Disease Control and Prevention—much lower rates than in Canada, the United Kingdom and Israel.

According to Axios, the more transmissible and dangerous Delta variant is moving quickly among unvaccinated communities and experts fear we’ll suffer another wave of infections.

“We’ve hit the wall in the number of vaccinations in recent weeks,” said Dr. Eric Topol, a noted cardiologist and founder of the Scripps Research Translational Institute. “Just trying to deduce from other countries where we’re headed, if we don’t get a big jump in our vaccination rate, we’re going to be vulnerable for a lot more cases.”

Topol adds that this would also mean more hospitalizations and death from COVID-19. While infectious disease experts vary on the percentage of vaccinated people needed to achieve herd immunity against COVID-19, it could be as high as 85% of the population.

Axios says that in April, data from the Centers for Disease Control and Prevention showed 4.4 million people got their shots in a single day. The national average has now plummeted to a mere 500,000 doses administered daily.

In order to boost the number of shots, President Biden announced yesterday that efforts will shift from mass vaccination sites to more user-friendly places, such as doctor’s offices, pharmacies, mobile clinics and employers.

One of the main groups that need to be targeted are adults between the ages of 18 and 30, said Dr. John P. Moore, professor of microbiology and immunology at Cornell University, according to Axios. Moore said that this age group often thinks they are “bulletproof,” and that they need to understand that “this bullet could hit you.”

Topol adds that there are two other groups of people that must be convinced. Some are hesitant to get the vaccine because it has not received full approval by the U.S. Food and Drug Administration, thinking that the emergency use approval or EUA means the vaccines were rushed through the system without full scientific testing. Moore points out that the gap between EUA and full authorization is a “distinction without a difference,” but some people may be more apt to get the shot when the FDA grants full approval.

The second group that may opt for putting off vaccines are the people who are mandated by their employers or schools, says Topol. Even though the federal government legally cleared the way in May for companies to require that their employees get vaccinated for COVID-19, many enterprises, including the military, have been reluctant to mandate shots.

A Kaiser Family Foundation poll conducted in May found that about one-third of Americans who are vaccine-hesitant said they would be more likely to get their shots if the vaccines received full FDA approval, according to The Hill.

Pfizer submitted data for full approval May 7 and Moderna applied June 1 for full approval of its vaccine. It is not known how long it will take the FDA to grant these requests.

“It would have a big impact on people getting vaccinated if it is FDA approved,” said Dr. Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security. “I think it’s worth asking why it hasn’t happened yet.”

Full approval may also pave the way for more employers to mandate vaccinations for their employees, according to The Hill. Dr. Kevin Tabb, president and CEO of Beth Israel Lahey Health, a large Massachusetts-based healthcare system, said that he understands that many of his staff would feel more comfortable if the EUA is lifted. “After the EUA is lifted, it will be a requirement that all staff be vaccinated against COVID-19 as a condition of employment.”