I remember a comparison of countries, something about Denmark and vaccines.
Actually that might've been about comparing autism rates US vs. Denmark, and doing something like comparing the numbers for new cases in one place to total cases in the other.
Searching for "infant mortality" on sgutranscripts.org it points to episode 510
, which has another story about vaccinations that does include infant mortality. Not sure that's what you're looking for, but it's the closest I can find atm.
Edit: I'm guessing that's not it. Do you remember any other details about the episode?