Delta Variant Wave

Analysis of Delta wave of Covid-19 that is coming From Stephan Dinan Nevada County  

As the Delta variant wave of Covid-19 surges, much of Nevada County doesn't seem to be taking it seriously. I thought it would be useful to share a deeper and specific analysis of the risks ahead. In my view, this is promising to be the most intense Covid-19 wave our county has yet faced which is doubly challenging since most people are far less cautious now. So I wanted to summarize the danger.

In Essence:

  1. The Delta variant will be much more formidable, especially for the unvaccinated, than the original variant last year, with close to twice the hospitalization rate overall
  2. It spreads twice as fast, meaning things are likely to move much quickly than previous waves
  3. Our numbers are now shooting up faster than when we headed to the last winter peak. We are likely to pass that peak in 2-3 weeks.
  4. Vaccinated people are not fully immune and can get symptomatic but typically milder cases and transmit to others
  5. A reasonable bet is that more than 1% of our County will be getting infected EVERY week beyond this point until the wave completes, which could well mean infecting twice as many as got it from the start of the pandemic to now (analysis below).
  6. We are likely headed towards hospital overwhelm based on the pattern we've seen in similar counties such as Lake County in California and Orange County in Florida. This will be dangerous for everyone and especially hard on healthcare workers
  7. There's going to be a lot of people who have their health compromised by Long Covid, which happens to about 1 in 10 people.

Some numbers to support the above statements:

  • On July 28, there were 68 new cases, which brings our trailing 7-day average to 21.1 per day, which is on the edge of the critical zone. Our highest 7-day average was on Dec. 9 at 63.
  • On July 8, we were at 5.4 new cases per day, which means our new cases per day has increased 3.9x in 20 days. If we continue at that growth rate, we'll be averaging 82 new cases per day in another 20 days, which actually seems conservative given the 68 new cases yesterday. Our test positivity rate is also on a steep growth curve at 7.2%, which indicates we're missing a lot of cases in the field and that it is spreading rapidly.
  • If we assume that there are at least 3x the cases in the field than are being caught by tests (a conservative assumption based on antibody studies) than we're talking about our known rate of 147 new cases per week (last week) actually being more like 450 cases in reality. When that doubles, by next week or the week after, we'll be at 1000 new cases in week, or 1% of the population of 100K   
  • So how many cases are possible? Right now, we have 48% of the county vaccinated and herd immunity for the Delta variant has gotten much higher (83% is a reasonable estimate). Partial vaccination doesn't seem to provide that strong of protection and even full vaccination is only 90%+ effective at preventing symptomatic cases (it's higher to keep you out of the hospital). In terms of immunity from previous infections, until now, we've had 5300 recorded cases - tripling that means maybe 15% of the county has a previous infection. If we assume 2/3rds of those retain enough antibodies and to ward off new infection, it still leaves us with a gap of about 30% or 30K people before we really hit herd immunity. If we assume there's another 10% possible in the vaccinated population (mostly mild), we end up with something like 34K potential new infections vs. 15K to date (very rough estimate). Given the increased rate of growth with the Delta variant, unless we dramatically change course, we're talking about up to 34,000 cases in a matter of 3 months. Put differently, 1 in every 3 people in the county could catch Delta in these next few months unless we change our behaviors.
  • If that scenario does happen, we'd end up with around 3600 cases of long Covid, or 3.5% of the county. Not only is that a personal burden, it's a heavy community burden on health care. I think it's very important for us to get sober about the impact on the county by looking at some parallel counties that are further ahead on the infection curve than we are. I find this helps us to not be in denial that this can only happen "somewhere else."