Adenovirus-Vectored Johnson & Johnson SARS-CoV-2 Vaccine: Reassuring Initial Results

Thus far, two SARS-CoV-2 mRNA vaccines have received Emergency Use Authorization, and two adenovirus-vectored vaccines are in phase 3 studies. In an industry-funded phase 1–2 study of one such vaccine, Ad26.COV2.S (Johnson & Johnson), investigators report findings following administration of this recombinant, replication-incompetent, adenovirus-vectored vaccine encoding a full-length SARS-CoV-2 spike protein. Healthy volunteers (age range, 18–55 [cohort 1] and ≥65 [cohort 3]; cohort 2 is in a longer-term study) received either low-dose (5x10¹⁰ viral particles) or high-dose (1x10¹¹ viral particles) vaccine in a single dose or two doses 56 days apart.

After vaccine administration in 805 participants (both cohorts) the most frequent adverse events were fatigue, headache, myalgia, and fever. Reactogenicity was lower in older individuals (cohort 3) and in those receiving the low dose. Neutralizing antibodies were present in 90% of participants on day 29 after the first dose (irrespective of dose and cohort) and reached 100% by day 57. CD4+ T-cell responses were also robust.