The rollout of a third dose of COVID-19 vaccine has sparked debate on ethical and political grounds, since a large swath of the human population has 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 the U.K. showed last week.
That suggests people with delta-induced breakthrough infections also may be capable of transmitting the virus, frustrating efforts to curb the COVID-19 pandemic. Waning antibody levels in some highly vaccinated populations such as Israel have prompted calls to offer boosters to blunt fresh waves of hospitalizations.