Thread by @bansisharma

1. Covid Mysteries

In India — where the Delta variant was first identified and caused a huge outbreak — cases have plunged over the past two months. A similar drop may now be underway in Britain. There is no clear explanation for these declines.

2. In the U.S., cases started falling rapidly in early January. The decline began before vaccination was widespread and did not follow any evident changes in Americans’ Covid attitudes. Maybe it was just reverting to previous year's decline after the holidays-induced surge.

3. In March and April, the Alpha variant helped cause a sharp rise in cases in the upper Midwest and Canada. That outbreak seemed poised to spread to the rest of North America — but did not.

4. This spring, caseloads were not consistently higher in parts of the U.S. that had relaxed masking and social distancing measures (like Florida and Texas) than in regions that remained vigilant.

5. Large parts of Africa and Asia still have not experienced outbreaks as big as those in Europe, North America and South America.

6. How do we solve these mysteries? Michael Osterholm, who runs an infectious disease research center at the University of Minnesota, suggests that people keep in mind one overriding idea: humility.

“We’ve ascribed far too much human authority over the virus,” he said.

7. The experience with Alpha in the Midwest this spring is telling. Even Osterholm said that he had assumed the spring surge would spread from Michigan and his home state of Minnesota to the entire U.S. It did not. It barely spread to nearby Iowa and Ohio.

8. Britain is another example. The Delta variant is even more contagious than Alpha, and it seemed as though it might infect every unvaccinated British resident after it began spreading in May.

9. Some experts predicted that the number of daily cases would hit 200,000, more than three times the Britain's previous peak. Instead, cases peaked — for now — around 47,000, before falling below 30,000 this week.

10. True, you can find plenty of supposed explanations, like the end of the European soccer tournament, the timing of school vacations and the Britain’s notoriously late-arriving summer weather. But none of the explanations would explain a boom and bust in caseloads in India.

11. A more plausible explanation appears to be that Delta spreads very quickly at first and, for some unknown set of reasons, peters out long before a society has reached herd immunity.

12. Andy Slavitt, a former Covid adviser to President Biden, says, “It seems to rip through really fast and infect the people it’s going to infect.”

13. This is not a nihilist argument. Human responses do make a difference: Masks and social distancing can slow the spread of the virus, and vaccination can end a pandemic.

14. The most important step has been the vaccination of many older people. As a result, total British deaths have risen only modestly this summer, while deaths and hospitalizations remain rarer in heavily vaccinated parts of the U.S. than in less vaccinated ones.

15. But the plea for humility does have policy implications. It argues for prioritizing vaccination over every other strategy. It also reminds us to avoid believing that we can always know which behaviors create risks. That lesson has particular relevance to schools.

16. Many of the Covid rules that school districts are enacting seem overly confident about what matters. Reopening schools unavoidably involves risk. The alternative — months more of lost learning and social isolation — certainly involves more risk and greater costs to children.

17. Fortunately, school employees can be vaccinated, and severe childhood Covid remains extremely rare.

18. We are certainly not powerless in the face of Covid. We can reduce its risks, just as we can reduce the risks from driving, biking, swimming and many other everyday activities. But we cannot eliminate them.

The End

[P.S. The above essay by David Leonhardt of NY Times.]