Reopening the Country - Some Musings on How I Think It Should Be Done and Why.

It is becoming increasingly clear that all over the country people are getting antsy about getting back to something at least approximating their normal life and freedoms.  At the same time, the government has caused us to pay a huge price in those freedoms and in the economy at all levels.  These sacrifices have allowed us to get to where we are now vis a vis the CoViD-19 pandemic (past the peak and seeing general reductions across the board, having never over taxed the hospitals - with the probable exception of a short time in New York City, NYC).  Every time I run my model, the cases, and the deaths jump like crazy when the restrictions are removed.  It seems obvious to me that to simply walk away from them would be irresponsible and foolhardy. 

However, every plan I've heard so far is based on being able to be reactive to the changes that come about as we reopen.  This is unreasonable for two several reasons: 1) we do not have the testing capabilities to determine who really has the disease, or who has had the disease, and 2) we know that the previous outbreak was circulating for an extensive period of time prior to it becoming obvious, thus making any reactive plan doomed to be too little, too late, and 3) doing lots of little steps would just spread the pain out over a longer time.

No, reactive plans are not the right approach.  We need a path where we can confidently calculate the risks and the outcome.  In other words, we need to be able to predict the outcome, not sit back and try to respond to it.  Happily, there are several recent reports that finally give us the data we need to be able to predict with a reasonable safety margin.

First, there have been several recent (and I use the next word loosely) studies that give us a reasonable handle on the true number of cases that have already happened.  There are (to my limited knowledge) at least five results that allow us to determine a number for the ratio of the total cases to the confirmed cases, R_cases.  The first is mentioned in my blog of April 7.  In this event, the entire town of Vo, Italy was tested for active virus.  Some simple math led to the conclusion that R_cases(Vo) ~ 130.  Next came a report from Chicago (see my blog from the 14th).  Here a drive through testing site tested for the presence of antibodies.  They reported that 30-50% of the people tested showed such antibodies.  In this case the math says that R_cases(Chicago) is in the range 110-190.  The third was from the hot bed of American CoViD-19 cases, non-other than NYC.  The R_cases(NYC) comes out to 33 (for details see my blog from the 16th). Finally, over the last couple days there are reports from Santa Clara County, CA and Chelsea, MA (the reports are here and here, respectively).  For these you can easily extract the ratios as R_cases(SCC) ~ 50-80  and R_cases(CMA) ~ 16.  Now there isn't any safe/practical/justifiable way to conflate these into one number, but I think a safe estimate is around 40.  All this implies very strongly that we are much farther on the way to developing herd immunity than anyone would have guessed just a few weeks ago, but how far?

It is quite easy to find data on the web that allows one to compute the relative infection rates for various age groups (in this case see this CDC page).  My calculation says that the infection rate (based on the number of confirmed cases) for those aged 0-18 is less than 0.02%, about 0.15% for those 18-45, 0.22% for those 45-65, 0.18% for 65-75 and 0.26% for those 75 and older (this is for a case load of about 497,000 confirmed cases - which was about April 10).   If we multiply these by 40, the actual infection rates can be estimated at 0.8%, 6%, 8.8%, 7.2%, and 10.4%, and these could easily be anything from a factor of 2 lower, to a factor of 4 higher.  Also the confirmed cases are now more like 700,000, so that's another factor of 1.4.  Nonetheless, we do not yet approach anything like herd immunity (except at the highest of the possible factors, and even then we'd be at something like 50%).

Second, the data now clearly tell us who can, with a relative safety risk, allow themselves to be exposed, and who should not.  All the data point very strongly to the disease being hardest on the elderly [I hate that that world applies to me... I really thought that getting old would take longer...] and those with significant underlying health issues, and is extremely dangerous for those who fall into both categories.  The relative death rates per 100,000 people in the same age groups as above are, less than 1, 11.3, 96.7, 311.7, and 778.8, respectively (from the NYC Health Dept CoViD-19 data webpage).  Based on some CDC numbers (which produce similar rate numbers) I can estimate that the rates for a breakdown of the 45-65 group into 45-55 and 55-65 would be something like 58 and 135. 

So how can we start to reopen as soon as possible?  Reopen slowly, with care, but only for age groups below 55 and only for those without substantial risk factors (see this CDC page, and links thereon).  These groups must do what they can to  keep the spread rate below about half of what it was, (still practice social distancing and extra hygiene practices).  This allows us to get a large fraction of the population back to work with minimal risk.  Even in a worst case (if there is less than 10% of the population currently exposed/immune and the spread rate is very high) the total number of additional deaths would almost certainly remain at or below what we have currently seen and the number of people stressing the health systems would likewise stay below the capacity of the system (the intrinsic death rates for these groups are more than 10 times less than for the most at risk age group, which completely dominates the current statistics, and if those with underlying conditions are removed from the 45-55 age group the death rate is likely to be well below the 58 quoted above).  The big risk in this plan is folks that have been 'reopened' may not keep a hard safe distance between themselves and those who are not reopened (and are much more at risk).  This is a real risk.

But, that's my plan. We would really want to emphasize over and over and over how important it is to not go see those who are still in isolation. We'd want to test as much as possible, and contact trace as well, but it really looks to be a plan that would result in less risk than a general reopening, and would have much less risk of really dire consequences. We'd definitely want to have grocery stores, etc, have special hours for those folks not in the reopened groups (and those folks would probably want to have as much as possible delivered or to arrange to pick it up).  People still won't get to go hug grandma and grandpa until a vaccine has been widely distributed, but such is life.