The really terrible pop-sci write-up says because the antibodies are smaller. The actual publication doesn't given a reason for using llamas. The rationale disc

The really terrible pop-sci write-up says because the antibodies are smaller. The actual publication doesn't given a reason for using llamas. The rationale discussed doesn't hold together, either, since nothing in the study is about "small ab penetrating deeper." To quote the actual study: "Moreover, most vaccine-induced antibodies are directed against the highly variable head region of hemagglutinin (HA) and are strain specific. However, broadly neutralizing antibodies (bnAbs) targeting influenza HA have been isolated and characterized (8). Several bnAbs have entered clinical trials as therapeutic agents, but their use in influenza prophylaxis remains elusive because of the incomplete coverage against circulating human influenza A and B viruses, which necessitates administration of a bnAb cocktail, and the need for multiple, high-dose injections for protection throughout the entire influenza season. High serum bnAb levels are required because of poor distribution to the upper airways. We present an alternative strategy for long-lasting protection in which single-domain antibodies (sdAbs) (9) with influenza A or B reactivity are linked together into a multidomain antibody (MDAb) and expressed at the nasopharyngeal mucosa through the intranasal administration of a recombinant adeno-associated virus (AAV) vector (10, 11) encoding the MDAb transgene." Their whole point was to take Ab that target highly-conserved regions and link them together into a, let's call it, multi-tool ab that has a variety of ways of hitting highly conserved regions. Nothing at all about that approach suggests using "smaller ab" to "penetrate deeper." It's true camelids produce single-domain antibodies which are much smaller than the multi-domain antibodies humans use, but that wasn't the goal of the study: on the contrary, using peptide linkers to string together ab sounds like it accomplishes quite the contrary. I think the actual rationale is: "we wanted to string together a bunch of different antibodies to maximize the likelihood of our construction finding a target, and human ab are so big that if we string them together it'll be useless - so we strung together a bunch of small, highly targeted ab, whose final size will still be small enough to allow the multi-headed hydra to interact with viruses."