Experts differ on need for Johnson & Johnson COVID-19 booster shot

The vaccine's single dose has been a major selling point.

The Johnson & Johnson COVID-19 vaccine has been pitched with one major advantage over its counterparts since it was authorized for use: It requires just one dose. But with the exponential spread of the highly transmissible delta variant, questions have arisen over whether recipients might need to "top off" their immunity against the now-dominant strain in the U.S. with a second shot. Although the J&J vaccine's efficacy at protecting against symptomatic COVID-19 in clinical trials was less than the two-dose mRNA vaccines from Pfizer and Moderna, it showed 100% effectiveness against hospitalization and death. Recent research suggests that mRNA vaccines, such as the Pfizer and Moderna, appear to hold up against the delta variant as long as you've been fully vaccinated with two doses. Pfizer reported Thursday that initial data showed that receiving a third dose, six to 12 months after being fully vaccinated, may give more protection and promised to have data to publish in the coming week to ask the Food and Drug Administration and Centers for Disease Control and Prevention to recommend a third dose.