Two South Korean hospitals are conducting experimental treatment on Middle East respiratory syndrome (MERS) patients, injecting them with blood plasma from recovering patients, the health ministry said on Tuesday, as four new cases were reported.

The procedure has been conducted on two consenting MERS patients in addition to existing care, the ministry’s head of public health policy, Kwon Jun-wook, told a media briefing.

Plasma treatment was previously used in SARS patients with some positive results in seriously ill patients that led to a decrease in the death rate by up to 23 percent, Kwon said.

Three years after the MERS virus first emerged in humans, there is no cure or vaccine that can protect people from falling sick with it, and little work has been done in develop a vaccine, despite considerable available scientific detail.

Four new cases were reported on Tuesday, bringing the total to 154 in the South Korean outbreak, the largest outside Saudi Arabia. The ministry also said three more patients with MERS had died, taking the South Korean death toll to 19.