We showed that activation and polarisation of CXCR5+ Tfh cells and CXCR5− memory T helper cells change in response to vaccination with the live‐attenuated yellow fever vaccine YF‐17D and that the frequencies of cTfh1‐polarised cells is predictive for the level of neutralising activity in the serum of vaccinees. This evidence concerns the gene CXCR5 and viral infectious disease.