Antispike IgG antibody decay after immunisation with fractional versus full booster doses of COVID-19 vaccines: A 6-month longitudinal analysis of the FRACT-COV trial in Brazil
Document Type
Article
Department
Paediatrics and Child Health
Abstract
Objectives: To compare antispike IgG levels over a period of 182 days of follow-up in healthy adults who received full or fractional booster doses of BNT162b2 or AZD1222 after completing a primary series of Sinovac, BNT162b2 or AZD1222.
Design: Double-blind, parallel-arm, phase IV randomised trial.
Setting: The study was conducted in Campo Grande, Brazil, and participants were recruited in neighbourhoods with the lowest booster vaccine coverage. Follow-up visits were home based.
Participants: 1451 (18-60 years) healthy adults who had received a full primary series of Sinovac (n=549), BNT162b2 (n=451) or AZD1222 (n=451) were included.
Interventions: Participants were randomised to receive booster doses of either full or fractional doses of BNT162b2, AZD1222 or a full dose of Sinovac in the Sinovac-primed group. Antispike IgG antibody levels were measured at 0, 28, 84 and 182 days post-booster.
Main outcome measures: Antispike IgG antibody levels were measured through blood samples at baseline and follow-up visits that were conducted 28, 84 and 182 days post-booster vaccination.
Results: Throughout the 182-day follow-up period, full doses of BNT162b2 generated the highest antibody titres compared with fractional doses and other vaccines in all primary groups. Full-dose AZD1222 compared with its fractional dose showed a substantial difference only at day 28. BNT162b2 fractional doses produced higher antibodies than AZD1222 full doses. Sinovac-primed participants had the lowest baseline antibody titres, with Sinovac boosters continuing to show low titres, compared with BNT162b2 or AZD1222 full or fractional doses.
Conclusions: Full doses of BNT162b2 consistently elicited higher antibody titres than fractional doses, AZD1222 and Sinovac at all time points. AZD1222 and Sinovac full doses produced lower titres than BNT162b2 fractional doses. Recommendations for using fractional doses of BNT162b2 as an alternative to full doses should be made cautiously, and further studies are needed to determine clinical protection levels.
Publication (Name of Journal)
BMJ Public Health
DOI
10.1136/bmjph-2024-002331
Recommended Citation
Verruck, J. B.,
Puga, M. M.,
de Oliveira, R. D.,
da Silva, P. V.,
Charu, V.,
Hedlin, H.,
Lu, D.,
Zhang, A.,
Ritter, V.,
Shaw, B.,
Rosser, J. I.,
Seidman, J. C.,
Carter, A. S.,
Qamar, F.,
Luby, S.,
Garret, D.,
Croda, J.
(2025). Antispike IgG antibody decay after immunisation with fractional versus full booster doses of COVID-19 vaccines: A 6-month longitudinal analysis of the FRACT-COV trial in Brazil. BMJ Public Health, 3(2), 1-8.
Available at:
https://ecommons.aku.edu/pakistan_fhs_mc_women_childhealth_paediatr/1604