Covid-19: How Does It End?

Let’s start with good news. In California, we have definitely “flattened the curve.” We are approximately 90% below my projections from the LAC data from 3/22 and 3/28. Our doubling time has significantly increased, and we are off our exponential curve.

I have been postponing putting out this aspect of my analysis for a week now. Everyday things seem to change, and I hoped my analysis would lead me elsewhere.  I want to spend a minute discussing what flattening the curve means,  what different aspects of the curve means and why I think we will have periods of self isolation/ social distancing and re-socialization over at least the next year.

The curve represents cases over time. The area under the curve represents the total number of cases.  By flattening the curve, we prevent hospitals from being overwhelmed. But it doesn’t mean we ”eradicate” the disease. We live in a globalized society where international travel still occurs and people can travel state to state.  If we don’t want to overwhelm the medical system and the number are correct, flattening the curve means we push out our time-line. It means this ends by one of three ways, we have a vaccine, we have an effective treatment or we reach herd immunity (which is thought to occur when about 2/3’s of the population has had the disease). 

Herd immunity, assuming the numbers are correct is several years away.  I think we will have a vaccine or treatment first.  So what does this mean?  I think it means we will go through multiple periods of social-distancing/ self isolation and re-socialization.  I’m hoping our numbers are wrong and that we are significantly underestimating the number of cases we have had. There are two main factors that give me hope.   In Iceland, half the people that have tested positive were asymptomatic and if Covid began in China in November and it has the transmissibility that it seems to have, hopefully many more people have had it than have realized it.
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Let's walk through a scenario below of how LA County could reach herd immunity without overwhelming the system, and you will see why I think we will have a vaccine or treatment before herd immunity and why this won't be over in a few months, but we will likely see multiple cycles of social distancing and re-socialization.  

We know that LA County has 10.1M people this means we need about 6.7M cases of covid to reach herd immunity. If we assume 5% of cases need a ventilator that means we will have 336,602. people needing a vent.  Average duration on vent has been variable depending on data-sets, but let's assume the average person who needs a vent requires it for 12 days. 336,602 x 12 is about 4M vent days required.  Gov. Newsom has called for 10,000 vents in CA, that means we should have about 2500 in the LA area.  If we divide 4M vent days by 2500 vents we will get the number of days required to reach herd immunity without overwhelming the system.  The answer is about 4 years.  That assumes we have our numbers of cases correct, which is a big if.  Harvard public health came out yesterday suggesting a similar scenario, though I am sure they had a much more eloquent model.  What this means if these numbers hold is that we have a long winter ahead, but with social distancing, we can prevent the system from being overwhelmed.

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Be well,

Amy