Munro APS, Janani L, Cornelius V, et al. - Researchers sought to generate data concerning the comparative safety and immunogenicity of different COVID-19 vaccines given as a third (booster) dose.

• Researchers conducted a multicenter, randomized, controlled, phase 2 trial of third dose booster vaccination against COVID-19 named COV-BOOST.

• Participants (aged older than 30 years) were randomized at least 70 days post two doses of ChAd or at least 84 days post two doses of BNT primary COVID-19 immunization course; further, the participants had no history of laboratory-confirmed SARS-CoV-2 infection.

• Splitting of a total of 18 sites was done into three groups (A, B, and C).

• Participants within each site group (A, B, or C) were randomly assigned to receive an experimental vaccine or control.

• COVID-19 vaccine or control was administered to 2,878 participants who met eligibility criteria.

• Either NVX-CoV2373 (Novavax; hereafter referred to as NVX), a half dose of NVX, ChAd, or quadrivalent meningococcal conjugate vaccine (MenACWY) control (1:1:1:1) was administered to participants in Group A.

• Participants in Group B were administered BNT, VLA2001 (Valneva; hereafter referred to as VLA), a half dose of VLA, Ad26.COV2.S (Janssen; hereafter referred to as Ad26) or MenACWY (1:1:1:1:1).

• mRNA1273 (Moderna; hereafter referred to as m1273), CVnCov (CureVac; hereafter referred to as CVn), a half dose of BNT, or MenACWY (1:1:1:1) was provided to participants in Group C.

• Per findings, antibody as well as neutralizing responses were boosted by all study vaccines after ChAd/ChAd initial course and by all except one after BNT/BNT, with no safety concerns.

• For ChAd/ChAd-primed individuals, study vaccines and controls had spike IgG geometric mean ratios (GMRs) ranging from 1·8 in the half VLA group to 32·3 in the m1273 group.

• For wild-type cellular responses compared with controls, GMRs ranged from 1·1 for ChAd to 3·6 for m1273.

• Spike IgG GMRs ranging from 1·3 in the half VLA group to 11·5 in the m1273 group were recorded for BNT/BNT-primed individuals.

• GMRs ranged from 1·0 for half VLA to 4·7 for m1273 for wild-type cellular responses compared with controls.

• For booster vaccination, policy choices will be made based on the substantial disparities in humoral and cellular responses, and vaccine availability.