Analysis of Neutralization Titers against SARS-CoV-2 in Health-Care Workers Vaccinated with Prime-Boost mRNA-mRNA or Vector-mRNA COVID-19 Vaccines.

With increasing numbers of vaccine-breakthrough infections worldwide, assessing the immunogenicity of vaccinated health-care workers that are frequently exposed to SARS-CoV-2-infected individuals is important. In this study, neutralization titers against SARS-CoV-2 were assessed one month after completed prime-boost vaccine regimens in health-care workers vaccinated with either mRNA-mRNA (Comirnaty, BioNTech-Pfzier, Mainz, Germany/New York, NY, USA, = 98) or vector-based (Vaxzevria, Oxford-AstraZeneca, Cambridge, UK) followed by mRNA-based (Comirnaty or Spikevax, Moderna, Cambridge, MA, USA) vaccines ( = 16). Vaccine-induced neutralization titers were compared to time-matched, unvaccinated individuals that were infected with SARS-CoV-2 and presented with mild symptoms ( = 38). Significantly higher neutralizing titers were found in both the mRNA-mRNA (ID: 2525, IQR: 1667-4313) and vector-mRNA (ID: 4978, IQR: 3364-7508) prime-boost vaccine regimens when compared to SARS-CoV-2 infection (ID: 401, IQR: 271-792) ( < 0.0001). However, infection with SARS-CoV-2 induced higher titers when compared to a single dose of Vaxzevria ( = 0.0072). Between mRNA-mRNA and vector-mRNA prime-boost regimens, the vector-mRNA vaccine regimen induced higher neutralization titers ( = 0.0054). Demographically, both age and time between vaccination doses were associated with vaccine-induced neutralization titers ( = 0.02 and = 0.03, respectively). This warrants further investigation into the optimal time to administer booster vaccination for optimized induction of neutralizing responses. Although anecdotal ( = 3), those with exposure to SARS-CoV-2, either before or after vaccination, demonstrated superior neutralizing titers, which is suggestive of further boosting through viral exposure.