Measles mortality fell markedly (>90%) from the 19th century to mid-20th century prior to introduction of measles vaccine or the widespread use of antibiotics for secondary bacterial infections [1][2] This story is similar for most infections we now vaccinate for, death rates were dropping dramatically years before vaccines were introduced.

[1] https://www.cambridge.org/core/journals/epidemiology-and-inf... [2] https://scholar.google.com/scholar_lookup?title=Measles+mort...