They're talking about the B-cells and T-cells created by the injected mRNA vaccines, which are certainly more or less permanent, and always waiting to be activa

They're talking about the B-cells and T-cells created by the injected mRNA vaccines, which are certainly more or less permanent, and always waiting to be activated on any future infection. Those are what prevent severe disease, but they don't prevent infection. The protection against severe disease from a 3-shot series of the mRNA vaccine is in all likelihood completely permanent. For the nasal vaccines to fail to produce that cellular immunity would be a massive failure. The short term durability of neutralizing antibodies seen with EVERY SARS-COV-2 VACCINE NOT JUST THE MRNA ONES is likely a feature of immunity to respiratory viruses. The "one series of shots to never contract the disease again in your lifetime" style of immunity probably doesn't exist for this virus. Certainly we don't know how to create one right now.