My Wife Has MS And Started On Tecfidara In January.

My wife has MS and started on Tecfidara in January. Her 'Absolute Lymphocites' in in two prior (before Tecfidara) blood tests were 1900 and 1400 per uL. Post Tecfidara they have been 1700, 1277 and most recently 800. Antibodies for JCV were not detected in the most recent test, but have been detected in the past. I know most patients experience about a 30% drop in lymphocites during the first year on Tecfidara, but can't help worrying about PML. My question is, given that her lymphocites have dropped 53% from January to May, should we continue monitoring or should she get off Tecfidara?