Viruses

Can anyone smarter than me give me some understanding of B cell depletion? I’m on Kesimpta for a year and just fought off RSV. I am now in hospital with my 3 year old who became severe and needs oxygen. We are sharing a room with another RSV patient who I believe is in full contagious mode and I’m wondering if I will catch it again?! I was under the belief that we develop no immunity to viruses once the B cells are killed?