The Supernatural Death Cough, or SDC, was the name given to the plague in Plague.
The SDC, unnamed at the time, was briefly mentioned in Lies. The virus exhibited flu-like symptoms that progressively worsened. Dekka, Cigar, Brianna and Jack had minor to moderate cases of the earlier stages of the virus.
The virus returns, but this time, kids cough so hard their inner organs are spewed out of their mouths.
Jennifer H. experienced a fit of coughing, which resulted in choking out a small fragment of her lung and dies soon after her. Jennifer B., exhibiting similar symptoms, crawls down to the hospital to warn Dahra of the deadly virus. Not identifying the threat, Dahra dismisses Jennifer B.'s warning as a feverish hallucination.
As time passes, more and more kids in the FAYZ fall ill or die to the SDC. Dahra estimates that roughly one in ten flu symptom cases will progress to SDC. To make matters worse, Lana (who has become an invaluable healer to the kids in the FAYZ) finds that her healing powers are ineffective against the virus and she is helpless to prevent it from spreading.