The filter removes all viruses known to cause trouble to the system.The last time I changed the canister I cracked it open (that's what boys do to understand how things work) and found nothing but charcoal.At one time they used an "Iodine Matrix" to eliminate viruses, but now it's apparently a secret!FYI & I quote from their website:"Independently certified to meet EPA Microbiological Purification Standards against cysts, bacteria & virus! Excels at chemical and aesthetic contaminant removal! No chemicals, hold time, or double pumping.""Super Easy Purification. First Need purifies naturally, without chemicals, hold time or electricity. Pure water when and where you need it!"