Immunogenicity of an mRNA-1273 vaccine booster in workers of a University Hospital in Colombia with a primary immunization schedule with BNT162b2: An ambispective cohort study

Abstract

Background: Combination of COVID-19 vaccines was a key strategy in countries with limited vaccine supply to achieve widespread coverage.

Objective: To determine the humoral immunogenicity of an mRNA-1273 booster in a group of hospital workers in Colombia who were vaccinated with a BNT162b primary scheme.

Methods: We conducted an ambispective cohort study in a university hospital in Bogotá, Colombia. The retrospective component was conducted as part of a previous study, where serum samples were drawn and stored, 4 to 44 days after completing a primary scheme with BNT162b. The prospective component began after the implementation of the vaccine booster in the country. We invited hospital workers with serum samples stored who then received an mRNA-1273 booster to participate in the study and prospectively monitored SARS-CoV-2 anti-spike IgG antibodies up to 10 months after the booster. We measured antibody titers in months 3, 6, and 9 after the booster. We compared antibody titers before and after the booster using a Skillings-Mack test, and assessed the factors related to the humoral response to the booster using a Random-effects Tobit regression model.

Results: We included 36 participants, 78% of them were women. Half of participants had previously presented COVID-19, and 53% displayed any comorbidity. The median of anti-spike IgG titers after the primary scheme was 3064,857 BAU/mL. Participants received the booster on average 267 days after the primary scheme. IgG titers peaked in months 3-4 after the booster (3459,361 BAU/mL). However, levels gradually decreased, with median titers of 3305.895 BAU/mL at 6-7 months and 3188.461 BAU/mL at 9-10 months after the booster (p-value= 0.0310). Age, obesity, and B-blood type were factors related to the humoral immune response to the booster.

Conclusion: An mRNA-1273 booster administered to individuals previously vaccinated with BNT162b generates a long-lasting humoral response, which is influenced by multiple host factors.