Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial

Introduction COVID-19 boosters restore waning immunity. After demonstrating non-inferiority of 15 μg versus 30 μg BNT162b2 at 28 days in Mongolian adults, we assessed 24-month immunogenicity and safety. Methods In this randomised, controlled trial, adults primed with ChAdOx1-S, BBIBP-CorV, or Gam-COVID-Vac were assigned (1:1) to 15 μg or 30 μg BNT162b2. Anti-spike IgG, surrogate virus neutralisation (sVNT) against Wuhan-Hu-1 and Omicron BA.1, and interferon-gamma (IFN-γ) release assays (Ag1/Ag2) were assessed to 24 months. SARS-CoV-2 infections and serious adverse events (SAEs) were recorded. ClinicalTrials.gov: NCT05265065. Results Of 601 participants, 520 (86.5%) completed follow-up. IgG and IFN-γ responses were comparable between arms at 24 months (IgG geometric mean ratio (GMR) 1.06 [95% CI 0.95–1.18]; Ag1 GMR 1.17 [95% CI 0.82–1.66]; Ag2 GMR 1.06 [95% CI 0.73–1.54]). Median sVNT inhibition remained high (Wuhan-Hu-1 88% [interquartile range (IQR) 86–90]; Omicron BA.1 85% [IQR 70–88]). Twenty-eight SARS-CoV-2 infections occurred. Fifty-three SAEs were balanced by study arm, and none were vaccine related. Discussion Equivalent immunity and safety from 15 μg and 30 μg BNT162b2 boosters support fractional dosing as a cost-saving strategy. Clinical Trial Registration https://clinicaltrials.gov/study/NCT05265065 , identifier NCT05265065.

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Journal
Frontiers in Immunology
Published
2026-03-23
DOI
https://doi.org/10.3389/fimmu.2026.1789248
Primary Topic
RNA Interference and Gene Delivery
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article
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article

Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial

Khaliunaa Mashbaatar, Shuo Li, Narantuya Namjil, Lkhagvagaram Batbayar et al.
Frontiers in Immunology
RNA Interference and Gene Delivery
article

Fractional BNT162b2 boosters induce durable immune responses after non-mRNA priming in Mongolia: a randomised controlled trial

Khaliunaa Mashbaatar, Shuo Li, Narantuya Namjil, Lkhagvagaram Batbayar, Paul V. Licciardi, Bolor Altangerel, Batbayar Ochirbat, Tsetsegsaikhan Batmunkh, Otgonjargal Amraa, Cattram Nguyen, Bilegtsaikhan Tsolmon, Nadia Mazarakis, Naranbaatar Avaa, John Hart, Kerryn A. Moore, Helen Thomson, Khulan Javkhlantugs, Claire von Mollendorf, Unursaikhan Surenjav, Khishigjargal Batsukh, Sarantsetseg Jigjidsuren, Frances Justice, Tsogjargal Burentogtokh, Kathryn Bright, Lien Anh Ha Do, Otgonbold Jamiyandorj, Kim Mulholland, Eleanor FG Neal, Gantuya Dorj
article en

Abstract

Introduction COVID-19 boosters restore waning immunity. After demonstrating non-inferiority of 15 μg versus 30 μg BNT162b2 at 28 days in Mongolian adults, we assessed 24-month immunogenicity and safety. Methods In this randomised, controlled trial, adults primed with ChAdOx1-S, BBIBP-CorV, or Gam-COVID-Vac were assigned (1:1) to 15 μg or 30 μg BNT162b2. Anti-spike IgG, surrogate virus neutralisation (sVNT) against Wuhan-Hu-1 and Omicron BA.1, and interferon-gamma (IFN-γ) release assays (Ag1/Ag2) were assessed to 24 months. SARS-CoV-2 infections and serious adverse events (SAEs) were recorded. ClinicalTrials.gov: NCT05265065. Results Of 601 participants, 520 (86.5%) completed follow-up. IgG and IFN-γ responses were comparable between arms at 24 months (IgG geometric mean ratio (GMR) 1.06 [95% CI 0.95–1.18]; Ag1 GMR 1.17 [95% CI 0.82–1.66]; Ag2 GMR 1.06 [95% CI 0.73–1.54]). Median sVNT inhibition remained high (Wuhan-Hu-1 88% [interquartile range (IQR) 86–90]; Omicron BA.1 85% [IQR 70–88]). Twenty-eight SARS-CoV-2 infections occurred. Fifty-three SAEs were balanced by study arm, and none were vaccine related. Discussion Equivalent immunity and safety from 15 μg and 30 μg BNT162b2 boosters support fractional dosing as a cost-saving strategy. Clinical Trial Registration https://clinicaltrials.gov/study/NCT05265065 , identifier NCT05265065.

Frontiers in ImmunologyVol. 17
Royal Children's Hospital (AU), The University of Melbourne (AU), Mongolian National University (MN), Tamedia (Switzerland) (CH), National Center for Communicable Diseases (MN), Mongolian National University of Medical Sciences (MN), El Paso County Public Health (US), National Centre for Infectious Diseases (SG), Innovation Initiatives Ontario North (CA)
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RNA Interference and Gene Delivery
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