Hi
sixxx,
how the AdCom perceives this move and whether it will have some impact (positive or negative) on the final decision will depend on whether this volunteer position is consistent with your application. For example, if your goals involve working in pharma in emerging markets and you're volunteering in Cameroon to provide medicine to people in need, then it could be seen positively.
It will also depend on how strong your profile and application are. If the school really wants you, the fact that you left your company at this point will probably make no difference to them. But if your application is a borderline case, it could help tip the balance. Whether in your favor or not, again, it depends.
In any case, the fact that you have been invited to interview is a clear sign that the school is interested in you. So just try to come up with a story that is consistent with your application.
Good luck!
Alex