Variation in the loop sequences - as observed in the SAFV-3(NL2007) isolate, which differs a single aa from other SAFV-3 strains in one of its VP1 loops (Fig. 3) - is in agreement with such a drift, but whether re-infections occur remains to be proven: Significantly higher antibody levels in adults, compared to children (Fig. 5), may suggest so but an increase in antibody levels may also be the consequence of infection by other members of the species (phenomenon of the original antigenic sin, OAS) [25]. The gene discussed is SMOC1; the disease is infection.