WASHINGTON (AP) — The Federal Bureau of Prisons says it has started to give the coronavirus vaccine to some high-risk inmates but won’t say how many inmates have been vaccinated or how it selects those to receive the vaccine.

The revelation, in a statement to The Associated Press on Tuesday, contradicts the agency’s previous policy that initial doses were for staff members. The AP reported last month that internal prison documents detailed that initial allotments of the vaccine “will be reserved for staff,” even though sickened prisoners vastly outnumber sickened staff.

“At this time, we can confirm high risk inmates in a few of the BOP facilities in different regions of the country have received the vaccine,” Bureau of Prisons spokesman Justin Long said in a statement.

Earlier on Tuesday, the agency said the vaccine had been delivered last week to four Bureau of Prisons facilities that had been among some of the hardest hit during the pandemic: the Federal Correctional Complex in Butner, North Carolina; federal medical centers in Carswell and Fort Worth, Texas; and FCI Seagoville, a low-security prison in Texas.

In the same statement, the agency said it initially planned to offer the vaccine to full-time bureau staff members, saying that vaccinating them “protects the staff member, the inmates at the facility, and the community.” The agency said about half of the staff at each of the four facilities had received the vaccine.

But later in the day, Long said that some inmates had also been vaccinated. The agency would not answer questions about how many inmates had been vaccinated, where they were housed or how it determines the criteria for who qualifies as a “high risk” inmate to be vaccinated. It is unclear how many doses of the vaccine have been delivered to the Bureau of Prisons.

The Bureau of Prisons said that the remaining doses sent to the four prisons “were provided to inmates based on priority of need in accordance with CDC guidelines.”

The agency has struggled for months to combat the exploding number of coronavirus cases in federal prisons across the U.S.

As of Tuesday, 5,929 federal inmates and 1,620 staff members had confirmed positive test results for COVID-19 nationwide and 29,313 other inmates and 2,718 staff had recovered from the virus, according to federal statistics. Since March, 171 federal inmates have died of the coronavirus.

At least two inmates scheduled to be executed by the Bureau of Prisons next month have also tested positive for coronavirus.