Humoral Response after a Fourth Dose with mRNA-1273 in Healthcare Workers with and without a History of SARS-CoV-2 Infection and Previously Vaccinated with Two Doses of BBIBP-CorV Plus BNT162b2 Vaccine.

There is limited information on the kinetics of the humoral response elicited by a fourth dose with a heterologous mRNA1273 booster in patients who previously received a third dose with BNT162b2 and two doses of BBIBP-CorV as the primary regimen. We conducted a prospective cohort study to assess the humoral response using Elecsys® anti-SARS-CoV-2 S (anti-S-RBD) of 452 healthcare workers (HCWs) in a private laboratory in Lima, Peru at 21, 120, 210, and 300 days after a third dose with a BNT162b2 heterologous booster in HCW previously immunized with two doses of BBIBP-CorV, depending on whether or not they received a fourth dose with the mRNA1273 heterologous vaccine and on the history of previous SARS infection -CoV-2. Of the 452 HCWs, 204 (45.13%) were previously infected (PI) with SARS-CoV-2, and 215 (47.57%) received a fourth dose with a heterologous mRNA-1273 booster. A total of 100% of HCWs presented positive anti-S-RBD 300 days after the third dose. In HCWs receiving a fourth dose, GMTs 2.3 and 1.6 times higher than controls were observed 30 and 120 days after the fourth dose. No statistically significant differences in anti-S-RBD titers were observed in those HCWs PI and NPI during the follow-up period. We observed that HCWs who received a fourth dose with the mRNA1273 and those previously infected after the third dose with BNT162b2 (during the Omicron wave) presented higher anti-S-RBD titers (5734 and 3428 U/mL, respectively). Further studies are required to determine whether patients infected after the third dose need a fourth dose.

Neutralizing Antibodies as Predictors of Vaccine Breakthrough Infection in Healthcare Workers Vaccinated with or without a Heterologous Booster Dose: A Cohort Study during the Third COVID-19 Wave in Peru.

We evaluated neutralizing antibody (NAbs) levels as a protective factor against vaccine breakthrough infection (VBI) in healthcare workers (HCWs) during the third COVID-19 wave in Peru. This retrospective cohort study employed the information from a private laboratory in Lima (Peru) of HCW who received only two BBIBP-CorV vaccines or (additionally) a heterologous booster with BNT162b2. We evaluated the association between the VBI and the levels of NAbs at 21, 90, 180, and 210 days after the BBIBP-CorV second dose. NAbs were calculated with the cPass™ SARS-CoV-2 Neutralization Antibody Detection kit (surrogate virus neutralization test (sVNT)) and the Elecsys® anti-SARS-CoV-2 S Test. Of the 435 HCW evaluated, 31.72% had an infection previous to vaccination, 68.28% received a booster dose, and 23.21% had a VBI during the third wave. The variables associated with a lower risk of VBI were male sex (aRR: 0.43) and those who had (180 days after BBIBP-CorV inoculation) NAbs levels ≥ 60% (aRR: 0.58) and ≥90% (aRR: 0.59) on cPass™, and ≥500 with Elecsys® (aRR: 0.58). HCW whose NAbs persisted at higher levels six months after the BBIBP-CorV showed a lower risk of suffering from a VBI during the third COVID-19 wave.