Has NYC peaked (again)?

January 15, 2021 By Alan Salzberg

We are at or past the peak of the second wave of COVID cases in NYC, meaning cases are beginning to slowly drop (deaths lag and will likely to continue to increase for a few weeks, unfortunately).  Before I explain why I believe this to be true, let's go back in time.

Nine months ago, on April 6, 2020, I wrote a blog that said NYC has peaked (NYC has Peaked).  That prediction turned out to be right.  Admittedly, at the time, things were pretty horrific, with hospitals and morgues overwhelmed, so it was perhaps not such a difficult prediction to say it was going to get better.  From that day, positivity rates (percentage of people testing positive for COVID) fell precipitously for weeks and continued a slower decline throughout the summer.  Using Brooklyn as an example, on April 6, the positivity rate was 56% (in all these figures, I am using 7 day averages to account for spotty reporting on weekends).  By May 1, it was 18%. By June 1, 3%.  By September 1, 0.9%.  

But then, as expected, the rate began to rise with people returning to work (and school, for a bit), and with the weather getting colder and people socializing indoors.  Still, just before Thanksgiving the rate was at a still manageable 2.2%.  Official case counts were around 500 per day.  Then it got even colder, and we had Thanksgiving, and we had Christmas.  The positivity rate went to 3.1% by 12/1, 4.2% by 12/15, and peaked at 6.4% (with confirmed cases around 1,800) on January 7.  

It has slowly dropped since then, and the 7-day average is now at 6.0% (with confirmed cases at about 1,500). 

The reason I believe this decline will continue (slowly) is that there is no other shock to the system on the horizon -- no big holidays that would cause a surge in travelers, no more sudden return to indoor activities -- afterall, it's the middle of the winter, we're not doing anything outdoors now that will suddenly become indoors, and no real prospect of everything here suddenly opening up to full capacity.

This means the decline we have seen is real, and represents a reproduction rate below 1, meaning we are no longer experiencing exponential increases in infections.

Are we at herd immunity?

Given our current behavior, the reproduction rate appears to be below 1, which is by definition herd immunity.  This means nothing more than if we continue our current behavior, we will not have an increasing rate of infections.  It does not mean infections will go to zero.  They will decline but getting to zero could take months or may never happen, as we continue to have people traveling back and forth and some people coming in with COVID.  Recall that in the summer, going from a 3% positivity rate to a 1% rate took three months.  Right now we are 6%, so it will take a while (without vaccines) to get back to rate summer rates of COVID.

So, yes, we're at a conditional herd immunity but if we all spent the next month at big parties, that would not be true.  It's only true in our current equilibrium-- I just don't see anything changing that equilibrium for the worse anytime soon.

How about the variant?

We now know the variant is here but it is currently only a very small percentage of cases.  With a reasonable amount of luck, by the time it becomes dominant, in late March or April, infections will be so low and vaccinations will begin to hit their stride to an extent that it wont matter. Also, it will be getting warm.  So, overall, it looks like the variant, even assuming it is 50% more transmissible (and that is still very much in doubt), will likely not have a huge effect.  If we get to next fall without having vaccinated most people, that's a whole other story, but for now, it's not a worry.

Let's end happy:

How about the vaccines?

They will help, a lot (but they are being delivered very slowly). The wise decision to begin giving them to everyone above 65 years-old essentially means deaths will drop 80% even at our current rates of COVID once the older folks are vaccinated.  And the additional people being vaccinated will reduce infection rates further.  So perhaps in late March we should begin seeing these serious effects.  I can hope it is earlier but we aren't vaccinating very quickly right now.

That's it for now!