Are We There Yet?

Sorry I’ve not been updating lately.  Life got busier and apparently I needed a break.

The great news over the last couple of weeks is that case numbers and death numbers have plummeted.  Cases have dropped from a high of 250,000 down to about 70,000 per day.  Daily deaths have dropped from 3,300 to about 2,000.  Here’s what the national chart looks like.

Beyond the drastic drop in both lines, there are two features to note.  

First, you probably have already noticed that both lines rise at the very end.  The death line in particular has a pretty sharp rise.  But notice that the two lines show this dip at the same time.  When both lines show a sudden change at the same time, that is an indication of an administrative issue.  Otherwise, changes in the death line lag changes in the case line by about two weeks.  That dip in the red line happens right at President’s day.  Lots of people had a long weekend and reporting was delayed.  That caused a sudden drop in reported deaths followed by an apparent rise once the reporting caught up.  California in particular had a spike of reported deaths on the 24th that accounts for about half of the apparent rise in deaths.  WIth that said, there is reason to think  that daily case rates are beginning to level off.  They will probably continue to drop some, but not as quickly as they have been.  This brings us to the second important feature.

Second, even with the dramatic drop, case rates are still what they were at the height of the summer surge.  We’re in far better shape than we were in December, but this is because of how terrible December was, not because we’re in great shape now.  I expect that we will see daily deaths continue to drop over the next two weeks as they also reach summer levels.  

So we’re roughly back to the stage we were when we were most panicked in July, but now we’re feeling good about it because we’ve been through even worse.  The biggest danger is that we will use this as an excuse to drop our guard.  We react to this situation based on how it compares to our recent memory.  If things are better than they were, we can feel that they are good.  The virus doesn’t do that.  It just spreads as it can.  The more of it there is around, the faster it spreads.  Another surge starting from our current level will be far worse than one starting from a lower level. We need to get back to the levels we saw in May rather than being content with where we are now.

What about herd immunity, all those cases and vaccines should make a difference, right?  Before I address this, let me be frank that this is an area on which reasonable people familiar with the data can disagree.  I’ll give you my view and reasoning, but there are bound to be people who know more than I do who are more optimistic and also those who are less optimistic.  The real answer is we don’t know.  We don’t know because this is a new virus with new variants and new vaccines.  We’ve learned a lot, so we can make educated guesses now, but they remain guesses rather than certainties.  Here’s my view.

I don’t think we have significant herd immunity yet and won’t for at least another couple of months.  Herd immunity happens when enough people have resistance that, on average, each infected person infects less than one other person.  So, 100 cases become 99, then 98 and so on.  Based on earlier estimates of how infectious COVID is we guess that at least 70% of people would need to be resistant.  The actual number is unknown, but I have seen estimates from 50% to 90% with most being toward the upper end of the range.

The CDC estimates that actual infection rates are 4.6 times higher than reported rates. ( ).  That would put actual infections at 131 million.  43 million people have had at least one dose of vaccine.  So at most, 174 million people have acquired resistance.  That would be about 53% of the population.  While that’s a lot of people, it isn’t enough.  Further, the actual number of people with resistance is likely far lower.

Vaccinations have rightly focused on the most vulnerable populations – those who are most likely to catch COVID and those who are most likely to develop severe cases.  Because of this, a large percentage of vaccinated people will already have had COVID.  Even if we gave vaccinations randomly, we would expect about one third of the people to already have had COVID. Given our focus on vulnerable populations, that number is far higher.  We don’t know how high, so I’m going to assume two thirds as a ballpark guess.  So only 14 million people acquired immunity from a vaccine, bringing the estimated total with resistance down to 145 million.

Next, vaccinated people require time to develop immunity.  At a minimum it takes two weeks after the first shot to really count as resistant.  Full resistance only comes a couple or more weeks after the second shot.  Thus far, fewer than half of the people who have had a vaccine have had two doses, fewer still have passed the two week mark after the second dose. Taking a guess at the numbers, and guesses are all we have here, let’s say that of the 14 million people who got a vaccine without already having COVID, 10 million have already developed substantial resistance.  That brings us to 141 million people being resistant, about 42% of the population and below even the low end estimates for herd immunity.

But wait, there’s more.  Our estimates for herd immunity are largely based on the original variant, Classic COVID.  Several new variants have been identified that are significantly more infectious that the classic version, so we really should be looking at the high end estimates rather than the low end, we really should be looking closer to 90% in my view.  Again, this is very much a guess, we don’t know what the real number is.

There are other factors to consider, for example the degree of resistance conferred by having COVID can vary quite a bit and seems to be lower than the degree conferred by being vaccinated.  But rolling everything together, my best guess is that we have around 40% of the population with substantial immunity and need around 90% before we actually have herd immunity.  We’re not halfway yet, we need about another 160 million people to either be vaccinated or infected.

Of course the population resistance we do have is enough to have some effect even if that falls below herd immunity.  Infection rates will be slowed somewhat as the virus encounters resistant people.  But at current levels, masks and social distancing are likely to have more impact than immunity does.  Masks and social distancing confer resistance through behavior rather than biology. If everyone wore masks, socially distanced, and practiced other preventative measures, that would effectively be the same as herd immunity.  The increase in these behaviors after the holidays is probably largely responsible for the rapid decrease in cases.  It’s helped by the increased immunity, but that immunity is still a minor factor in my view.  It will become a bigger factor as more people are vaccinated and have time to develop immunity, but at current rates that will be summer at least.

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