Could be an immune response to exposure to spike protein shedding, but this is pure speculation on my part. I had some tooth work done recently, and they took x-rays, and said oh by the way my sinuses above my upper teeth are almost completely filled with fluid. Who knows how long that's been like that. I also use an iodine-based nasal spray every time I feel something coming on, and it's extremely effective at knocking things out before they become a full-blown cold.