I suspect that the serum is proprietary, expensive, and experimental. Until it passes clinical trials and is patented, drug companies don't want to risk giving it away to competitors. And governments don't want to be accused of experimenting on foreign patients with untested drugs. Many powerful serums are deadly toxic at the wrong dosage or in the presence of other factors. Big lawsuits could result. I think these knowledgable medical professionals signed a lot of exculpatory documents before being allowed the medicine as a special exception.