More than 20 million healthcare workers are among the first Americans scheduled for vaccination pending clearance by the Food and Drug Administration for the Pfizer drug.

But, according to Stateline, a division of Pew Charitable Trusts, only one-third of a panel of 13,000 nurses said they would voluntarily get inoculated. Another third said they would not get the vaccine and the remaining third said they were on the fence, according to the American Nurses Association.

Hospitals and other healthcare facilities said that if nurses and other medical professionals continue to decline getting the vaccine, they may consider mandating the shot, like the flu vaccine.

One nurse interviewed said the only reason she gets the flu vaccine annually is because it is required by her place of work.

“Some healthcare professionals may not necessarily want to be the first to roll up their sleeves,” Dr. Georges Benjamin, executive director of the American Public Health Association said, according to Stateline.

Dr. Susan Bailey, president of the American Medical Association, said that once physicians see the science behind the vaccines and have access to that data, more will come around in favor of vaccination.

However, a November poll conducted by the Pew Research Center found that 39% of Americans said they would also decline the vaccine because of fear it was politically fast-tracked. Experts say that if healthcare workers lead the way, more of the general public in the U.S. will follow suit.

“Skepticism about something as new as this vaccine is reasonable whether you are a healthcare worker or not,” said Dr. William Schaffner of Vanderbilt University. “It will be very important for healthcare providers to get the vaccine so they can model the behavior and personalize their stories.”

It’s the first time vaccinations in the U.S. have used mRNA technology, so experts still have many questions about the short- and long-term potential side effects.

Dr. Moncef Slaoui, the leader of the Trump administration’s vaccine program for COVID-19 called Operation Warp Speed, said that both Pfizer and Moderna’s drugs are safe but produced noticeable side effects in 10% to 15% of people who received the vaccine in clinical trials.

According to CNBC, those who did suffer side effects reported redness and pain at the infection site along with fever, chills, muscle aches, and headaches.

“The longer, more important kind of adverse events such as autoimmune disease or others have not been reported in a different way between the placebo group and the vaccine group in these two trials, which is very reassuring,” Slaoui said.

But even short-term, debilitating side effects can be problematic for hospital workers, according to Stateline, because the facilities are already short-staffed. The Centers for Disease Control and Prevention’s advisory committee suggested that hospitals avoid vaccinating everyone in the same department at the same time.

Legal experts say that while it would be preferable that healthcare workers voluntarily get the COVID-19 vaccine, it may still be mandated in the future like the flu shot and other vaccines.