Zeynep Tufekci writes:

If world leaders don’t act now, the end of the Covid pandemic may come with a horrible form of herd immunity, as more transmissible variants that are taking hold around the world kill millions.

There’s troubling new evidence that the B.1.617.2 variant, first identified in India, could be far more transmissible than even the B.1.1.7 variant, first identified in Britain, which contributed to some of the deadliest surges around the world.

In countries with widespread vaccination, like the United States and Britain, we can expect that Covid cases, hospitalizations and deaths will continue to decline or stay low, especially because lab tests and real world experience show that vaccines appear to defend recipients well against the severe effects of both variants.

For much of the rest of the world, though, this even more transmissible new variant could be catastrophic.

The evidence is not yet conclusive because the data is preliminary and figuring out if a variant is more transmissible isn’t easy. It could be spreading rapidly in an area because of chance. Maybe it got there before other variants and found a susceptible population, or got lucky and seeded a mega-cluster. If a variant is seen more frequently in a country’s genomic databases it could just be because travelers, who are often tested more routinely, are bringing it in from another country where it is already dominant.

One key measure that’s been used in previous outbreaks to figure out if a variant was more transmissible was to look at “secondary attack rates” in non-travel settings — how many people who come into close contact with an infected person get the virus themselves. The greater the number of these contacts getting the virus, on average, the greater the likelihood that a variant’s transmissibility is greater.

Data on secondary attack rates released on Saturday by a British public health agency similar to our own Centers for Disease Control and Prevention suggests that this variant first seen in India may be substantially more transmissible among close contacts than even the already highly transmissible B.1.1.7. A report published by the same agency on Thursday further supports last week’s findings. It was just such early data that raised alarms about B.1.1.7, with later information confirming those early fears. [Continue reading…]