Thanks for your response! You bring up some great points.

1. Unlike the age thresholds which are easier to define, severe chronic disease is a more nebulous concept. Exactly which people with chronic disease are at risk is a big question right now because so much data is lacking. For now, I will comment that when it comes to other infectious diseases and how they affect chronically ill patients, there is a significant difference in how well controlled their chronic disease is. A patient with diabetes and an A1c of 13 (A1c is a measure of diabetic control) is at a lot higher risk for infectious complications than if the A1c is. say, 7.5. Same with asthma. A patient with intermittent asthma who uses her rescue inhaler 1–2 times per month is much lower risk for complications of pneumonia than a patient with severe asthma on a biologic agent and 3 other controller medications who averages 3 hospitalizations per year. Thankfully, only a small portion of Americans with chronic disease fit into the severe/uncontrolled category which likely confers the highest risk for complications of COVID-19. But, it’s important to note that the details on this are not yet clear. It will take quite some time before the effects of COVID-19 on patients with chronic disease are fully parsed out.
2. Yes, you are exactly right on the timing. We can’t have 80% of the population, even if its the healthiest 80%, become infected all at once. Even though the virus is super contagious, I don’t think we are in danger of that happening. My guess (this is just a guess because no one really knows) is that the soonest 80% of the population could be exposed would be within about 6 months. What we also don’t want to happen is for it to take 2–3 years to get to 80% exposure and herd immunity and have to isolate the vulnerable group for such a long period of time. It’s hard to know what percent are requiring hospitalization right now because testing is still disproportionately weighted towards sicker patients, but as antibody testing ramps up I think we will see those hospitalization percentages go down. There was a small study in New York on that recently that was far from conclusive but still interesting. https://www.nytimes.com/2020/04/23/nyregion/coronavirus-antibodies-test-ny.html
3. Avoiding exposure for the vulnerable group hasn’t been easy thus far and will continue to be difficult regardless of how everything plays out. Common sense will be vital. Even in circumstances where full isolation is unavoidable, taking reasonable precautions to protect the high-risk group such as wearing masks, hand washing, cleaning surfaces, etc. can still reduce risk of transmission and even reduce the inoculum of exposure (we don’t know if reducing the number of virus particles in an exposure helps reduce COVID-19 severity but until we find out, it can’t hurt to try). While I think widespread contact tracing may be overkill for a virus that is almost certainly going to become endemic no matter what we do, contact tracing will continue to have value in regards to minimizing exposure to high-risk people particularly those grouped together such as those in nursing or assisted living facilities. As you alluded, antibody testing will be helpful for family members and caretakers of vulnerable people. Even if they were never symptomatic, those who have developed immunity to SARS-CoV-2 are most likely very low risk to transmit it.

Thanks again and please feel free to share more anytime!