How Delta Is Bolstering the Case for Covid Boosters

Covid-19 booster shots are being rolled out in the U.S. and other countries in response to waning antibody levels in already vaccinated individuals, and the increased threat posed by the hyper-infectious delta variant of the coronavirus that causes the disease. Giving a third shot to healthy people is a contentious strategy, since many low- and middle-income countries have yet to immunize even a tenth of their population. From a scientific standpoint, though, there’s mounting evidence that it could help stem transmission and avert hospitalizations and deaths.

Antibodies are needed to neutralize or block the virus, called SARS-CoV-2, before it can invade the cells lining the nose and throat, where it first replicates to cause an infection. Numerous studies have reported a reduction in antibody levels over the six months following full immunization. But the degree to which that occurs with Covid shots appears to vary depending on factors including: