Tuesday, April 21, 2020

COVID-19 Testing, Herd Immunity and Vaccines

Let’s talk about the ‘normal’ flu for a moment.  Actually there isn’t a normal flu.  Apparently there are many versions.  Each year somebody guesses which strains are going to hit and tries to target our annual vaccine to those strains.  Usually we hear the vaccine is 30 to 60% effective.  I’m not sure whether that means the vaccine doesn’t work against the targeted strains or whether they guessed wrong on which strains to vaccinate against.

Let’s stay on flu for a bit longer.  Have you ever heard of anyone getting a flu test to see whether they have a flu virus?  I would guess if you go to a hospital, they might administer a test.  How about anybody ever getting an antibody test to see if they have recovered and are immune to another bout?  You might assert we have herd immunity from those who’ve been sick and those who get the vaccine?  Then why do 20,000 to 60,000 die each year from the flu?  Maybe the medical community doesn’t think the costs of additional testing will have any benefit?

Now to COVID-19. I initially heard there were two strains of the virus.  The last report I saw indicated a dozen strains.  Now, not being medical, nor having seen the reports, I cannot say what that means to potential vaccine effectiveness or to potential herd immunity.  I am not making any claim that COVID-19 is just another flu.  What I am doing is trying to make some points about expectations on handling COVID-19.

First, even if we get a vaccine or vaccines at 12 or 18 months, or even at 6 months, we shouldn’t expect it to be more than 30 to 60% effective.  I would rough that out to mean if you get a vaccine, you’ve only reduced your risk by about 50% if you are exposed to the virus.  Every bit helps, and I would still like to get a vaccine.

Now, would you like herd immunity?  That would mean enough of us are immune so a seed of the virus couldn’t spread.  Obviously a good thing if it can be achieved without a lot of people dying.  From our experience with multiple strains of the flu, limited flu vaccine effectiveness, and known rates of people willing to get a vaccine, herd immunity seems unlikely to happen.

Let’s look at herd immunity from a different perspective.  I’ve seen reports that to achieve herd immunity (e.g. with measles or mumps) you have to get 60% of a population immune or vaccinated.  We’ve already touched on vaccinations.  What about through normal spread?  They say it’s much more contagious than the flu (although I haven’t seen any evidence or data); so let’s assume that is true.  Further, they say the worst cases are so much worse than the flu; maybe.  But the point I’m making is that fear has caused us to shut down the economy and hide.  People are accused of being heartless and murderers if they congregate or go around without a mask.  The result is that we have done everything possible to slow the spread of the virus and prevent herd immunity.

So my conclusion is that both vaccine promise and potential herd immunity are questionable.  We need to get on with life and learn to live with COVID-19.

Now I want to touch on testing for a moment.  A couple of blogs back I pointed out my views on widespread testing—not that helpful.  But that was a macro view.  What about the micro view?

Suppose you have a county with 1,000 cases and 50 deaths up to now.  You’ve got at least one mid-sized city and 200,000 people.  You are still seeing a dozen new cases every few days.  You’ve been on shelter-in-place with non-essential businesses closed.  Let’s say the governor is letting the county manager do their own thing.  30% of your workers are out of business with nearly all small businesses closed and at risk of bankruptcy.  You want to start opening again, but everyone is saying you need extensive testing.

What are the considerations?  Current testing constraints say you can only test 0.5% of your population each week.  If you let only recovered or immune back to work, you can only let 1,000 people go back to work now.  You can start broadening testing up to 1,000 people per week.  Assuming all those are negative or have antibodies, you can open up at a rate of 1,000 per week.  With 30% unemployment, that might be 1,000 out of 30,000 people.  It would only take 6 months to get everyone back to work.  And that’s if you only tested healthy, unemployed working age people.

But what about customers for the stores you open?  Do they get tests?  You don’t have enough.  What about the regular workers not out of work.  Do they get tested?  What about contact tracing for new cases, do you test them too?

If the government is able to get more testing supplies, maybe they can double the testing in a month or two.  It’s not clear to me that any significant quantity of large-scale testing machines are being built.  Do we want to wait 2, 3 or 6 months with a closed economy until we can get huge numbers of people tested?  I don’t.  And I sure haven’t seen any testing capability in the past that says we can actually achieve that goal.

Stop reading these and get on with your life.  Be safe!

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