24 Nov Evaluation of SARS-CoV-2 infection risks after primary vaccination with BNT162b2, BBIBP-CorV, or ChAdOx1-nCOV-19 and after homologous and heterologous booster vaccinations with these vaccines and evaluation of SARS-CoV-2 reinfection profiles
S. Djorwe , A. Bousfiha ,N. Nzoyikorera , J. Nyandwi , B. Kawthar , A. Malki
Abstract
Background: The emergence of SARS-CoV-2 variants has significantly increased the number of cases of COVID-19
among vaccinated individuals, raising concerns about the effectiveness of current vaccines. The aim of this study was to
analyze the SARS-CoV-2 infection risks after primary vaccination with BNT162b2, BBIBP-CorV, or ChAdOx1-nCOV-19
and after homologues and heterologous booster vaccinations with these vaccines, as well as the profiles of reinfected
patients.
Methods: We analyzed retrospectively 1082 patients vaccinated or unvaccinated with BNT162b2, BBIBP-CorV, and/or
ChAdOx1nCoV-19 vaccines to determine their SARS-CoV2 infection statuses using the reverse transcription-polymerase
chain reaction (RT-PCR) in addition to their clinical features. The infection risks of patients receiving the different
vaccine regimens were compared using multivariate logistic regression analysis, comparing the adjusted OR of a pos
itive COVID-19 test result.
Results: Among 596 vaccinated patients, 53%(n ¼ 286) tested positive for SARS-CoV-2 and 57%(n ¼ 310) tested
negative. Among positive cases, 10 were reinfection cases. The risk of SARS-CoV-2 infection was 1.6 (adj. OR) for pa
tients who received one dose compared with those who received two doses (95% CI ¼ 1.3e1.8; p < 0.01).The risk was 2.6
(adj. OR) for patients who received one dose compared with those who received three doses (95%CI ¼ 2.1e3.3; p < 0.01),
and 1.6 (adj. OR) for patients who received two doses compared with those who received three doses (95% CI ¼ 1.3e2;
p <0.01). The patients who received two doses that were heterologous to that of the primary vaccine had the lowest risk
of infection. Booster vaccinations (third dose) significantly reduced the number of positive cases with an acceptable
safety profile. Higher cycle-threshold (Ct) values (indicative of viral load) were observed in vaccinated patients, whereas
low Ct values were observed in unvaccinated patients.
Conclusion: A complete cycle of vaccination with homologous vaccines or heterologous vaccines resulted in an
acceptable reduction in SARS-CoV-2 infection. Further, vaccination was associated with a reduction in viral load.