The platform trial in COVID-19 priming and BOOsting (PICOBOO): The reactogenicity of nine licensed COVID-19 vaccines delivered in immunocompetent adults.

BACKGROUND: PICOBOO is a randomised, Bayesian adaptive trial evaluating immunogenicity and reactogenicity of licensed COVID-19 vaccines in immunocompetent individuals aged >12 years. We present reactogenicity data for nine vaccines administered as additional doses within adult strata based on age cohort and primary vaccination regimen. METHODS: Individuals who had not received a COVID-19 vaccine within three months were eligible. Participants were randomised within each stratum to receive a single vaccine dose. Reactogenicity events were recorded on days 1-7 following vaccination. Serious or medically attended adverse events (AEs), AEs of special interest, and AEs resulting in withdrawal were collected through day 28. Participants were followed until day 720. FINDINGS: A total of 1049 COVID-19 vaccine doses were administered to 586 adults enrolled between March 2022 and September 2024. Of these, 335 (57%), 96 (16%), 97 (17%) and 58 (10%) were randomised one, two, three and four times, respectively. At least one local reaction was reported after 786 (75%) doses and at least one systemic reaction after 798 (76%) doses. Local reactogenicity ranged from 47% (110/236) with NVX-CoV2373 (Nvx) to 90% (131/145) with Moderna, while systemic reactogenicity ranged from 69% (162/236) with Nvx to 85% (121/143) with BNT162b2. Pain was the most common local reaction; headache, fatigue, myalgia, and chills were the most common systemic reactions. Severe reactogenicity events were rare. INTERPRETATION: Reactogenicity events were common but rarely severe. Although reactogenicity appeared less frequent following Nvx than mRNA vaccines within strata, the trial was not powered for between-vaccine comparisons and findings should be interpreted descriptively. FUNDING: Medical Research Future Fund (2014690/2016473) and The Snow Foundation.