No vaccine is of any value when the average lifespan is 40 years due to lack of clean water and sanitation. This is a proven FACT, not a medical OPINION.
Medicine is an art based on opinions and consensus, it is not a science.
Let's put it this way: every medical advance has an effect on lifespan. Sanitation helped to prevent the spread of diseases like cholera and giardiasis. Vaccines, for the most part, help to prevent the spread of highly communicable viral diseases. Ensuring food safety (through proper cooking and preservation) helps to prevent potentially lethal food poisoning. Etc. Each of these measures decreases the incidence of infectious disease, and every decrease in infectious disease results in longer average lifespan.
IIRC, as little as a decade ago, infectious disease was still responsible for over half of deaths worldwide. Even now, it is one of the top ten killers.
Medicine is an art based on opinions and consensus, it is not a science.
Really? Then why does the US government spend billions of dollars on medical research every year?
Where the "art" comes into the practice of medicine is in the interpretation of the evidence. The physician uses scientific measures and experience to make the best determination of what is wrong (and can be mistaken, since there are many many things that can go wrong with the human body, and tracking down what they are can be very challenging).