  Aim. Our aim is to analyse the variance of the Inter-Galactic Medium
transmission (IGM) by studying this parameter in the rest-frame UV spectra of a
large sample of high redshift galaxies. Method. We make use of the VIMOS Ultra
Deep Survey and the VANDELS public survey to have an insight into the far UV
spectrum of $2.7<z<6$ galaxies. Using the SPARTAN fitting software, we estimate
the IGM towards individual galaxies and then divide them in two sub-samples
characterized by a transmission above or below the theoretical prescription. We
create average spectra of combined VUDS and VANDELS data for each set of
galaxies in seven redshift bins. Results. The resulting spectra clearly exhibit
the variance of the IGM transmission that can be seen directly from high
redshift galaxy observations. Computing the optical depth based on the IGM
transmission, we find an excellent agreement with QSOs results. In addition,
our measurements seem to suggest that there is a large dispersion of redshift
where complete Gunn-Peterson Trough happens, depending on the line of sight.
