No one is contesting the role of nutrition, working conditions, and sanitation in infectious diseases generally. What I asked was: what evidence is there that this is a significant contributor to infectious disease in countries like the US? (I should clarify that I'm referring to present-day US, because we're discussing in context of MAHA which is present-day US)

Yes, measles death rates had dropped precipitously (fortunately), however incidence (new cases) had only dropped a little. It wasn't until the vaccine was introduced that incidence dropped to nearly zero[1]. Yours is a common anti-vaxx talking point, and one that seems to neglect that death is not the only negative outcome from measles. It's understandable to take the talking point at face value when it appears to be scientifically-supported, though this is a good example of how a talking point uses a cherry-picked fact and reframes the issue for a presupposed conclusion (that vaccines are unsafe or ineffective), because the origin of that talking point had no interest in comprehensively informing people but converting them to believers.

[1] https://ourworldindata.org/grapher/measles-cases-and-death-r...