On Thursday, @EzraKlein published an important column with discouraging news: the new variants of the corona virus will make it far more difficult to end the pandemic and return to life as we knew it in 2019.

https://www.nytimes.com/2021/01/28/opinion/new-covid-strain.html

1/N

The new variants will make life worse even if they have a fatality rate that is no worse; and even if the available vaccines work just as well against them.

It is bad enough that the new variants spread so much more easily.

2/N

I have been working all day to put together some calculations to support the numbers that Ezra quoted from me. The hold up has been that the closer I look, the worse things look.

3/N

I do not want to raise undo alarm, and I'm having trouble coming up with realistic scenarios that do not involve hundreds of thousands of additional deaths in 2021.

4/N

I can reinforce one of Ezra's points: it is extremely important that we speed up the pace of vaccinations to 3m shots per day. But as I explain below, even this will leave us in a very dangerous position this summer, one that will probably force us to do even more.

5/N

Why 3m per day? The B.1.1.7 variant will have fully taken over in the US in about 20-25 weeks, at the beginning of summer. At that point, R0 will have increased to somewhere in the range 4.5-5.2.

6/N

If we vaccinate 70% of the pop, we will end up with a susceptible fraction of about S = 0.2 (because many people are already protected by a previous infection.) At the pace of 3m shots per day, we protect 1.5 million people per day (because everyone has to get two shots.)

7/N

So at 3m shots per day, we get a susceptible fraction that is down to S = 0.2 in about 22 weeks -- the beginning of the summer -- just as R0 is reaching its steady state value around 5.0.

8/N

I may be too pessimistic, but I expect that by this summer, people will no longer be diligent about wearing masks. Nor will they be willing to accept continuing activity restrictions. Bars and restaurants are likely to be open.

9/N

So this summer, I expect that the effective R will the product of the new higher R0 and susceptibility of about S = 0.2, unaffected by mask mandates and activity restrictions. Of course, this means that we will just barely get to an effective R that is equal to 1.0.

10/N

If the US takes twice as long -- 44 weeks, into November -- to vaccinate down to S = 0.2, it will will face many weeks during the summer and fall with an effective R that is greater than 1.0, and will therefore face a new exponential wave of infections and deaths.

11/N

With 3m vaccinations per day, if R0 increases to just 5.0, we just barely avoid a prolonged period of time with an effective R greater than 1.

12/N

But if R0 is even bigger -- 5.2 perhaps -- S = 0.2 will imply R > 1.0. We will then face a choice between committing indefinitely to measures that limit the spread of the virus or accepting a new wave of infections (and deaths it will cause) as the way to get S below 0.2

13/N

It will not surprise you that the additional policy measure I recommend for limiting the spread of the virus is test-and-isolate.

14/N

What is a shock for me is the prospect that we will want to keep relying on test-and-isolate even after we have vaccinated 70% of the population.

15/N

If we can sustain the pace of 3m per day, it looks like testing everyone once every two weeks would leave us with an buffer that keeps us well away from 1.0. Testing at this frequency would reduce the effective R by roughly 20% (that is, by a factor of 0.8.)

16/N

If we can only do 1.5m shots per day, we might need to test people more frequently -- once a week. This would reduce the effective R by a factor of 0.5, which should be enough to get us through the summer and fall without a new wave of infection and death.

17/17