Thank-you for commenting Timbo!
The best answer for 3rd-world conditions would be better infrastructure, specifically sanitation, along with a well-rounded diet. Vaccines aren't going to make a malnourished person healthy.
If my children ever decided to travel someday somewhere filthy and diseased, they can make their own decisions on vaccines as an adult. I believe that with research on what the threats in that location are, they could probably just bring along proper water cleaning systems, and/or certain supplements that are known to prevent that specific affliction.

A person does have to be very careful with travel vaccines and getting everything recommended. For example a neighbour of my mother's, a young woman, came down with Guillain Barre Syndrome and was hospitalized for a long time because of her vaccines for a trip to Africa. I think that she would have been better off taking her chances in Africa without the vaccines, or just not going at all if she had known the risk of the vaccines. As it was, she had to cancel the trip anyways since she was hospitalized.