I don’t know about you but as an ecologist, I am not an expert in disease dynamics nor part of the inner community rapidly exchanging ideas and data. But as an ecologist I have a better handle on notions of population growth, species interactions, individual encounter rates, etc than the average population (and probably the average scientist) and I have felt in a frustrating vacuum of information.
To address this, we’re trying something new here at Dynamic Ecology – an open thread, the main purpose of which is to have a place for the community to have a conversation. Our comments sections have long been the most interesting part of the blog, so now we’re creating a direct path to comments without your having to read 1000s of words of bloviation from me!
First, a few thoughts to give some common terminology/framing to the questions. I think ecologists all know about the power of exponential growth (although this is new and still poorly grasped to most of the world). R0 is the discrete growth rate with no immunity (naive population) and no efforts at social distancing. Best estimates I have seen for Covid 19 is about R0=2.5 which is a good bit higher than flu (and a good bit lower than measles). It seems to be becoming clearer that R0 is as high as it is because people can be infectious before they show symptoms (or even if they never show symptoms like children). Once immunities start to build up or quarantine/social distancing measures start to be put in place a lower growth rate Re (effective growth rate) is observed. So as far as I can tell there are three strategies.
- Squeeze it – extreme social distancing to reduce Re<1. This seems to be what China as well as Japan and South Korea are doing (probably not coincidentally all Asian countries that got hit most by SARS and MERS).
- Let it burn – do nothing to lower Re=2.5. Sadly many (all?) countries started down this road – with exponential growth the speed of reaction required seems to be faster than governments can handle.
- Stretch it – social distancing to get Re~1.2 (nb 1.2 is an example, not a carefully calculated number, just a wild guess proxy as it is about what influenza does) so that the case load does not exceed hospital capacity. This is what everybody is talking about as “flattening the curve”.
With the stretch it and let it burn strategies the number of people who get sick and then have immunity rises to about 1-1/R0 or about 60% of the population (assuming getting sick once confers immunity – assumed right now but a few counter examples are out there). Then the effective growth rate Re drops below 1 and “herd immunity kicks in”. Individuals can still get sick but it can’t become a self-sustaining epidemic. The primary difference between let it burn and stretch it is the rate at which people get sick which is inversely correlated with how long the epidemic lasts.
I’ve posed several questions below to get this started. I’m not an expert. So the answers to some of these may be obvious in which case, I’d love to know the answer. But I have not seen the answers to any of these despite voracious reading. If they’re not so obvious I expect we could all learn from discussing them.
If you want to respond to a question stay in the same thread (even if the nesting stops at 3 levels). If you want to pose a new question, start a new thread. This is NOT a place for politics, so anything stronger than “many governments have been incompetent at X” (e.g. naming specific individuals, blaming one party or another, or getting distracted off science) will be deleted.