Why Delta Might Be a Good Variant

I’m no epidemiologist, but it occurred to me that there might be a silver lining with the COVID-19 Delta variant.

  1. Delta is explosively contagious, with an R0 between 6 and 9. This means that the average infected individual is expected to transmit Delta to 6 and 9 additional people (versus 2.5 for COVID-19).
  2. This means that it just rips through populations. Because it can be transmitted by the vaccinated, it can travel deeper across the population as well.
  3. But so far is has not been found to be more lethal than the original, except to the extent that it crushes hospital capacity with its surge.
  4. Think about the virus’ evolutionary goals. It doesn’t actually care whether people live or die – the variant that spreads best dominates. If Delta manages that, while letting the vaccinated largely be unharmed, then it could become the pandemic’s endpoint.
  5. Why? Delta might crowd out new variants if it gets around and becomes the primary endemic version. To defeat Delta and take its dominant position, the next variant would have to be even better at spreading.
  6. Of course that is possible, but if Delta already can be spread by the vaccinated, it’s possible that is has already maximized the population growth prospects for this kind of virus in humans. The vaccinated can carry a Delta population in their nose without realizing it.
  7. Ironically, if any current vaccine were perfect, it would leave an attack surface for the next variant – conquer the vaccine. Perhaps the optimal vaccine simply allows us to live with the Coronavirus and welcome it to the family of standard household colds?
  8. And so perhaps Delta has evolved to be well suited to our current vaccines, able to maximize its reproduction. If we are lucky, it will crowd out any more lethal strains – marking the beginning of the end of the pandemic. There’s some indication that this might be happening, as Lambda has been present for some time, but has yet to grow in the US to extent that Delta has.
  9. This all assumes that vaccination efforts eventually meet with success and cover the overwhelming majority of the human population.

This could be wishful thinking – new variants will either validate or make a mockery of it soon. But the explosive growth and subsequent subsidence in COVID Delta cases in the UK and India give me room for hope!

Coronavirus: Why the US Might Fare Better than Expected

Update 5/31/2020 – It’s been two months exactly since this post. Some aspects have aged well – US deaths to date did in fact peak around 2500 per day, and the rate of death has declined substantially since. The notion that we’d stay below 100k deaths overall has not, however. I believed that the opportunity created by April shutdowns would be used to ramp testing 10x, and that mask usage might dramatically increase. It now appears that the US is instead focusing on a vaccine as the only solution, with ongoing deaths the price paid for an unwillingness to wear masks or test aggressively.

Original Post – 3/31/2020

With the steady drumbeat of negative news, it’s easy to slip into despair about the state of the nation and the world. The present moment has enabled journalists and well-meaning prognosticators of all sorts to shout out the depth of our peril. While the danger is real, I’d like to take a moment to point out a myriad of reasons why the Coronavirus pandemic may end in something less than the worst case outcome (for the skeptical, you will find ample sourcing along the way).

First, let me define what I mean: a worst case outcome would be something approximating the Imperial College of London study, with millions of deaths in the United States. While President Trump initially stalled and downplayed the crisis, the response is now rolling nationwide, with 75% of the US under lockdown and 90% of Americans saying that they are staying home in some manner. If the US manages to traverse a path similar to that of Italy, we might keep total fatalities at or below 100,000.

Italy Coronavirus Status as of 3/30/2020:

Italy entered a nationwide lockdown on March 9th, and the positive results of this action have become evident over the last 10 days (roughly two weeks after lockdown). Worldometer’s Coronavirus charts tell a striking story – new Coronavirus cases as of March 30th are below that of March 19th, and total daily deaths remain below the peak set on March 27th. While the trend could yet reverse, this follows the path set by China  in which strong lockdown measures resulted in a drop in new cases a bit under two weeks later. If Italy’s trends continue, coronavirus should become less lethal in the country once the curve is sufficiently flattened and hospital capacity is again able to deal with all critically ill patients.

US Favorable Metrics Relative to Italy (and China):

The US has the dubious distinction of having the world’s most Coronavirus cases, but we also have quite a few factors working in our favor. Let’s walk through each and then apply an Italy-style scenario to the US:

  1. The population density for the lower 48 is roughly 329M / 3.1m sq miles = 106 people/sq mile, versus 533 people / sq mile in Italy. This is not a linear factor as populations are grouped into much denser metro areas, but in general metro area density in the US is still much lower than in Italy.
  2. 22.7% of Americans are above the age of 60, versus 29.8% of Italy. Since the vast majority of Coronavirus deaths are of those beyond the age of 60, this factor alone should reduce America’s risk by 25% relative to Italy.
  3. There is some early statistical evidence that sun, warmth, and absolute humidity might reduce the spread of Coronavirus. According to these models, the later onset of the outbreak in the US and warmer climate (relative to northern Italy in early March) could prove ameliorating.
  4. Results of testing every individual in the village of Vo, Italy revealed that for every positive test in a broader population, up to 10 times as many individuals may have contracted the virus. These kinds of results indicate that the mortality rate might stabilize below the current 1% estimate.
  5. Over 50 different drugs or treatments are currently being investigated – the worst case scenarios imply that all of these treatments fail or are so delayed that they prove ineffectual.
Summing it up, what’s the potential outcome?

Since the US has now instituted many of the measures put in place in Italy and elsewhere, let’s assume that we follow Italy’s lead. President Trump extended initial “social distancing” guidance on March 16th, but most of the US did not follow suit until March 23rd (when restaurant, school, and other closures became widespread).

Italy started a full lockdown on March 9th as noted earlier, roughly 14 days before the US entered a partial lockdown. Let’s assume that the US didn’t achieve anything approximating full lockdown until March 30th – this would place the peak of the epidemic in mid-April, following the Italian pattern of a 2-week delay. Italy appears to have peaked under 1,000 deaths per day  – this would equate to roughly 5,000 deaths per day in the United States if conditions were equivalent. As mentioned earlier, age distribution alone lowers risk by 25%. US density is 80% less than Italy, but let’s assume this reduces peak impact by less than half that, taking our overall risk relative to Italy down to 50%. This would imply 2500 deaths per day at peak.

Italy sustained roughly 4,000 deaths prior to hitting the current plateau March 20th – if they remain at these levels for 30 days before descending, that would lead to another 30,000 deaths, followed by another 4,000 if the descending phase mirrors the ascent. This would represent a conservative outlook relative to China, which stayed on a plateau near peak death rates for only two weeks.

If the United States follows Italy’s lead, we might experience 8,000 deaths climbing to the peak, 75,000 deaths on the peak plateau (30 days at 2500 deaths/day), and a similar number on the way down – for a total number of deaths just under 100,000. These estimates assume the net positive impact of climate, treatments, and lower mortality rates is zero.

Does this sound like fantasy? Italy is already beginning to look optimistic that it is turning the corner, with new cases down from the peak – and it’s quite possible that the United States is just a few weeks behind, provided we keep the doors shut, stay at home, and let the storm pass, while we get our testing and treatment capabilities ramped up.