study published on July 19 on the medical journal website BioRxiv found that the single-dose Johnson & Johnson vaccine was significantly less effective against the highly transmissible delta and lambda variants compared with two-dose vaccines from Pfizer and Moderna.
Study authors found that while the two-dose vaccines were 94-95% effective in preventing COVID-19, the J&J vaccine had only 66.9% efficacy "in preventing moderate to severe disease." The study compared the efficacy and drop-off rate of antibody protection from all three vaccines and found that neutralization of the delta and lambda variants decreased with the J&J vaccine.