Auto open vista and keep the focus with autocmd

[Wombozo]

Is it possible to open vista with autocmd, but without losing the focus ? The two commands :Vista followed by :Vista focus work great but not inside autocmd...

augroup VistaAutoOpen
      autocmd!
      autocmd BufRead *.c,*.h  Vista | Vista focus
augroup end

Expected behavior
Vista automatically opens when opening .c and .h files, and then focus back to the source file.

Actual behavior
The focus remains on the side window.