The observation of gravitational waves by the three LIGO-Virgo interferometers allows the examination of the polarization of gravitational waves. Here, we analyze the binary neutron star event GW170817, whose source location and distance are determined precisely by concurrent electromagnetic observations. We apply a signal accumulation procedure to the LIGO-Virgo strain data and find that the measured LIGO-Livingston signal is substantially reduced in certain frequency intervals due to real-time noise subtraction. We obtain ratios of the signals detected by the three interferometers excluding these depleted regions from the data analysis. We find that the signal ratios are inconsistent with the tensor polarization predictions of general relativity and Einsteins theory is ruled out at 99% confidence level. Moreover, we find that the signal ratios and distance to the source are consistent with the vector theory of gravity (Phys Scr 92:125001, 2017) and that vector GW polarization is favored over tensor polarization and scalar polarization with exponentially large Bayes factors. If, however, we erroneously include in the data analysis the frequency regions in which the Livingston signal is depleted by noise filtering, we reproduce the result of the LIGO-Virgo collaboration favoring tensor GW polarization over vector polarization with an exponentially large Bayes factor.