HealthDay News — A candidate vaccine, Ad26.COV2.S, with a recombinant, replication-incompetent adenovirus serotype 26 (Ad26) vector encoding a full-length and stabilized severe acute respiratory syndrome coronavirus 2 spike protein is safe and immunogenic, according to a study published online Jan. 13 in the New England Journal of Medicine.
Jerald Sadoff, M.D., from Janssen Vaccines and Prevention in Leiden, Netherlands, and colleagues conducted a phase 1-2a trial involving healthy adults ages 18 to 55 years (cohort 1) and 65 years or older (cohort 3). Participants were randomly assigned to receive Ad26.COV2.S at a low dose or high dose or placebo in a single-dose or two-dose schedule.
The researchers found that the most frequent adverse events were fatigue, headache, myalgia, and injection-site pain after administration of the first vaccine dose in 805 participants in cohorts 1 and 3 and after the second dose in cohort 1. Fever was the most frequent systemic adverse event. Systemic adverse events were less common in cohort 3 versus 1 and for those who received a low versus high dose. On day 29 after the first vaccine dose, neutralizing antibody titers against wild-type virus were detected in 90 percent or more of all participants; this level reached 100 percent by day 57, with a further increase in titers irrespective of vaccine dose or age group. Until at least day 71, the titers remained stable. An increase in the titer by a factor of 2.6 to 2.9 was seen with a second dose. Spike-binding antibody responses were similar to those of neutralizing antibodies.
“Our interim analysis indicates that vaccine candidate Ad26.COV2.S is safe and immunogenic in both younger and older adults,” the authors write.
The study was funded by Johnson & Johnson, the manufacturer of the Ad26.COV2.S vaccine.