Step by step, Kendal has been moving closer to a state of “post-Covid normality”, with fewer restrictions and less need for masks and social distancing. It’s not clear whether we will be able to continue that progress, however. The new “Delta” variant is to blame.

Breakthrough cases on the rise. Recent articles about “breakthrough” infections in vaccinated people have gotten my attention. The first was an article from Slate about a family, fully vaccinated, that got together for a Florida vacation. They thought they would be OK without masks, but all the adults got sick by the time they returned home. The second was an article from the New York Times about people who were among the 60,000 who attended a huge July 4th celebration in Provincetown, MA, and then got sick. At least 900 tested positive for Covid (mostly the Delta variant), and the majority of them were fully vaccinated.

What’s going on here? The leading theory is that people infected with Delta shed hundreds of times more virus than people with earlier variants, and that massive shedding apparently overcomes the immune response created by the vaccine. Still, vaccination works to reduce the severity of the infection, and vaccinated people who get Delta rarely end up in the hospital (there were just four instances of this in the Provincetown cluster). So vaccination is very important, but it is not a total solution.

The importance of transmissibility. The Delta variant is much more transmissible than earlier Covid variants. That means an infected person is much more likely to pass it on. Estimates by the New York Times suggest that while a person with the earlier versions would be likely to infect 1-3 other people, a person with Delta would be likely to infect 5-9 others—some of whom may well be vaccinated. It also appears that vaccinated people who get Covid are themselves quite infectious. 

I first read of this transmissibility issue in a piece by Tomas Pueyo two weeks ago, and his warning is being borne out in the rising case numbers.

One implication of heightened transmissibility is that it will be much more difficult (or perhaps impossible) to reach “herd immunity”, the state at which immunity is so widespread that the disease peters out.

Kathleen Neuzil, a vaccine expert at the University of Maryland School of Medicine, was quoted in the Washington Post as saying. “It’s hard to do, but I think we have to become comfortable with coronavirus not going away.”

In other words: we may find Delta behaves like the flu, returning periodically forever.

Our local situation. The situation in Chester County is better than in many parts of the country, but there are ominous signs. The County rate of PCR test positivity, a measure of how many of those tested actually have Covid, is at 2.84% as of Friday, July 30. It has been rising steadily (from below 1% a few weeks ago), which is concerning. But it is well below 5%, which is roughly the threshold at which widespread community transmission would be suspected.

On the other hand, the incidence of Covid infection in our County has been rising rapidly. Two weeks ago, it was at 7.05 per 100,000 of Chester County population. A week ago, it was 17.91 per 100,000. Now, it is 26.48 per 100,000. That’s higher than the US average (about 22 per 100,000) and high enough to rank two notches above the minimum level on the New York Times “Covid Hot Spots” map.

Given the uncertainties in both the national and local situations, it wouldn’t be too surprising if we have to put our “re-opening” process on hold—or even begin reversing it. It depends on how serious the threat from Delta turns out to be.