Another Vector Question

Do different strains of the simfluenza act differently? My child sim had strain 3. She had a 2 day germy moodlet and vomited about 3 times during the first 24 hours. To my surprise, about 24 hours after her illness started, I received a notification that she had recovered. But when I checked on her, she now has a 3 day germy moodlet, and she has gotten up to vomit 3 times in the night, so far. I did not get any notification that she had come down with a different strain or had a relapse. Her mother and her toddler sister have also come down with it, and both have 3 day germy moodlets.