Q: Please explain how the Jansen (J&J) vaccine is effective when it is one shot, not two.

The J&J vaccine was studied as a single dose vaccine and a 2-dose vaccine; the 2-dose study (called ENSEMBLE-2) is still being performed, but is anticipated to definitively demonstrate improved efficacy compared to the single dose. Nonetheless, the single dose J&J is very good at preventing hospitalization and deaths. The Astra Zeneca vaccine (a 2-dose vaccine) and J&J vaccine are both very similar to each other and use the virus-vector approach to make the vaccine.

Response by E. Albert Reece, MD, PhD, MBA, Executive Vice President for Medical Affairs, UM Baltimore, John Z. and Akiko K. Bowers Distinguished Professor, Dean, University of Maryland School of Medicine


Wilbur H. Chen, MD, MS, FACP, FISDA, Professor of Medicine, University of Maryland School of Medicinem Chief, Adult Clinical Studies section, Center for Vaccine Development and Global Health (CVD), Director, UMB Travel Medicine Practice