biostudies-literatureYao AJiangsu Provincial Science Fund for Distinguished Young Scholarshe National Natural Science Foundation of China750https://www.ebi.ac.uk/biostudies/studies/S-EPMC12103785biostudies-literatureUnknown25(1)<h4>Background</h4>A two-dose primary regimen of INO-4800 DNA vaccine demonstrated only modest immunogenicity in the previous phase 2 clinical trial. This booster study aimed to evaluate the immunogenicity and safety of a booster dose of INO-4800 in adults previously received two-dose regimen of INO-4800.<h4>Methods</h4>Healthy adults who received two doses of INO-4800 (1.0 mg or 2.0 mg) at least 12 months ago in a previous phase 2 trial were eligible for this booster study, conducted in Danyang, Jiangsu Province, China. Eligible participants were stratified by primary vaccination dose (1.0 mg or 2.0 mg) and age group (18-59 years or ≥ 60 years), and subsequently randomized in a 1:1 ratio to receive a third dose of INO-4800 or placebo at the same dosage as previously administered. The primBMC infectious diseasesImmunogenicity and safety of a booster dose of the COVID-19 DNA vaccine in healthy adults aged 18 years and above: a single-center, randomized, observer-blind, placebo-controlled phase 2 trial.PMC1210378582341031, 82173584, and 82222062BK20220064Yang HXia YXu MLi JLeng DWang BCheng XWang JXu JPan HJia SHuai XZhao GYao AWang ZfalseImmunogenicity and safety of a booster dose of the COVID-19 DNA vaccine in healthy adults aged 18 years and above: a single-center, randomized, observer-blind, placebo-controlled phase 2 trial.<h4>Background</h4>A two-dose primary regimen of INO-4800 DNA vaccine demonstrated only modest immunogenicity in the previous phase 2 clinical trial. This booster study aimed to evaluate the immunogenicity and safety of a booster dose of INO-4800 in adults previously received two-dose regimen of INO-4800.<h4>Methods</h4>Healthy adults who received two doses of INO-4800 (1.0 mg or 2.0 mg) at least 12 months ago in a previous phase 2 trial were eligible for this booster study, conducted in Danyang, Jiangsu Province, China. Eligible participants were stratified by primary vaccination dose (1.0 mg or 2.0 mg) and age group (18-59 years or ≥ 60 years), and subsequently randomized in a 1:1 ratio to receive a third dose of INO-4800 or placebo at the same dosage as previously administered. The prim2025-01-01T00:00:00Z2025 May2026-06-02T02:43:40.634Z2026-04-13T03:12:34.277ZS-EPMC121037854041485110.1186/s12879-025-11140-w