The Children’s Hospital of Philadelphia will soon require all its on-site employees to be vaccinated against the coronavirus, as most of their patients are too young to receive the COVID-19 vaccine.

The hospital did not specify a deadline for employees to receive the vaccine, but said in a statement Thursday that it is “currently preparing for the implementation of a vaccine requirement.”

“We believe that it is our duty to protect those who cannot protect themselves, especially our young patients,” the statement read.

The move would make CHOP the second major health care system in Philadelphia to mandate the vaccine for employees, after Penn Medicine.

» READ MORE: Penn Health System takes the lead in requiring employees to be vaccinated against COVID-19

In a memo sent to staff members, CHOP officials wrote that they had initially planned to mandate inoculation once the COVID-19 vaccines were fully licensed by the Food and Drug Administration.

But they changed those plans given the rise of the more contagious delta variant, which now accounts for most cases in the United States, and cited concerns that continued spread of the virus would mean even more contagious variants could develop.

» READ MORE: Full FDA approval of COVID-19 vaccines might lead more people to get them. What’s the holdup?

About 70% of CHOP patients, officials wrote in the memo, are not yet eligible for the vaccine, which is only available to those age 12 and older. They noted that most COVID-19 infections, hospitalizations, and deaths are now occurring among the unvaccinated.

In addition, they said, at the height of the pandemic, when community spread was high, most of the COVID-19 exposures at CHOP occurred among its employees, emphasizing the need for a hospital-wide mandate.

“We have a responsibility to our patients, our colleagues, and our communities, and we must act now,” officials said.

CHOP already mandates flu vaccines for employees, and follows CDC guidelines for vaccine requirements and infectious disease screening for employees, said Camillia Travia, a CHOP spokesperson.

The move came as another area hospital system, ChristianaCare in Delaware, announced that it will also require its caregivers to be vaccinated for COVID-19 by Sept. 21. (The health system defines “caregivers” as ChristianaCare employees, medical-dental staff, residents, students, contracted employees, temporary labor, volunteers and vendors.) The only exemptions will be for “specific medical conditions and religious beliefs,” health system officials said in a statement.

“We believe we have reached a tipping point at which the urgent need for all caregivers to be vaccinated is clear,” said Neil Jasani, the hospital’s chief people officer.