From Jason Crawford, Emergent Ventures winner in Progress Studies:
…the surprising thing I found is that infectious disease mortality rates have been declining steadily since long before vaccines or antibiotics…
In 1900, the most deaths came from tuberculosis, influenza/pneumonia, and gastroenteric diseases such as dysentery. All of these were effectively conquered by antibiotics in the 1930s and ’40s, but were on the decline since at least the beginning of the century…
Indeed, digging further into the UK data from the late 1800s, we can see that TB was declining since at least 1850 and gastroenteric disease since the 1870s. And similar patterns hold for lesser killers such as measles, which didn’t have a vaccine until the 1960s, but which by then had already declined in mortality by more than 90% from its 1900 levels.
So what was going on? If you read my survey of technologies against infectious disease, you know that other than drugs and immunization, there is one other way to fight germs: cleaning up the environment.
I was surprised to learn that sanitation efforts began as early as the 1700s—and that these efforts were based on data collection and analysis, long before a full scientific theory of infection had been worked out.
There is much more at the link, including the footnotes for citations to the claims made here.