Moreover, with a view to mitigating VAERD risk in seronegative children, preclinical studies should assess the four key immune properties recommended by WHO: (1) the ability to induce anti-RSV nAb, (2) the capacity to avoid generating non-nAbs and have a low binding IgG/nAb ratio, (3) the prevention of strong Th2-type CD4+ T cell response, and (4) ensuring the absence of alveolitis following a valid live RSV challenge. Here, CD4 is linked to hypersensitivity pneumonitis.