  The strong coupling between molecules and photons in resonant cavities offers
a new toolbox to manipulate photochemical reactions. While the quenching of
photochemical reactions in the strong coupling regime has been demonstrated
before, their enhancement has proven to be more elusive. By means of a
state-of-the-art approach, here we show how the \iso{trans}{cis}
photoisomerization quantum yield of azobenzene embedded in a realistic
environment can be higher in polaritonic conditions than in the cavity-free
case. We characterize the mechanism leading to such enhancement and discuss the
conditions to push the photostationary state towards the unfavoured reaction
product. Our results provide a signature that the control of photochemical
reactions through strong coupling can be extended from selective quenching to
improvement of the quantum yields
