The case for a booster shot is building, even if privileged few get it

The roll out of a third dose of Covid vaccine has sparked debate on ethical and political grounds, since a large swath of the human population is yet to receive any inoculation. But the case for boosters on scientific grounds is building.

The reason is delta. The most-infectious coronavirus variant to emerge so far is in a race with the human immune system, and there’s mounting evidence that delta is winning -- at least initially. Fully vaccinated individuals infected with the variant have peak virus levels in the upper airways as high as those lacking immunity, a large study from