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two patients receiving the higher fingolimod dose died of herpes zoster infections, disseminated in one case and causing encephalopathy in the other. Increased rates of herpes zoster infections were also seen in the other fingolimod trial and with cladribine

Varicella zoster virus can become latent in the nerve cell bodies and less frequently in non-neuronal satellite cells of dorsal root, cranial nerve or autonomic ganglion, without causing any symptoms. Years or decades after a chickenpox infection, the virus may break out of nerve cell bodies and travel down nerve axons to cause viral infection of the skin in the region of the nerve. The virus may spread from one or more ganglia along nerves of an affected segment and infect the corresponding dermatome (an area of skin supplied by one spinal nerve) causing a painful rash. Although the rash usually heals within two to four weeks, some sufferers experience residual nerve pain for months or years, a condition called postherpetic neuralgia. Exactly how the virus remains latent in the body, and subsequently re-activates is not understood.

Throughout the world the incidence rate of herpes zoster every year ranges from 1.2 to 3.4 cases per 1,000 healthy individuals, increasing to 3.9–11.8 per year per 1,000 individuals among those older than 65 years.

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From Wikipedia:
Herpes zoster (or simply zoster), commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe. The initial infection with varicella zoster virus (VZV) causes the acute (short-lived) illness chickenpox, and generally occurs in children and young people. Once an episode of chickenpox has resolved, the virus is not eliminated from the body but can go on to cause shingles—an illness with very different symptoms—often many years after the initial infection.

Macular edema had been seen with fingolimod in previous transplantation trials, and there were 4 cases of suspected macular edema in this trial (1 since the month-24 analysis). However, the diagnosis was not confirmed by external review of retinal specialists. There was some elevation of hepatic enzymes, but as had been seen with other adverse events, the frequency declined over time, Dr. Comi noted.
"All of these data taken together continue to suggest that the drug is active; second, the frequency of adverse effects tends to decrease with continuation of the treatment, and there was no evidence of any new adverse effects except some reports of skin malignancies," he said.

Seven cases of skin malignancies were observed during the extension trial: 3 basal-cell carcinomas, 2 squamous-cell carcinomas, and 2 melanomas. All were in situ, and all have been treated without other complications, he said.