Effectiveness of Heterologous Coronavirus Disease 2019 (COVID-19) Vaccine Booster Dosing in Brazilian Healthcare Workers, 2021

Abstract

Objectives Little is currently known about vaccine effectiveness (VE) for either two doses of Oxford-AstraZeneca (ChAdOx1) viral vector vaccine or CoronaVac inactivated viral vaccine followed by a third dose of mRNA vaccine (Pfizer/BioNTech) among healthcare workers (HCWs). Methods We conducted a retrospective cohort study among HCWs (aged ≥18 years) working in a private healthcare system in Brazil from January to December 2021. VE was defined as 1-IRR (incidence rate ratio), with IRR determined using Poisson models with the occurrence of laboratory-confirmed COVID-19 infection as the outcome, adjusting for age, sex, and job type. We compared those receiving viral vector or inactivated viral primary series (two doses) to those who received an mRNA booster. Results A total of 11,427 HCWs met the inclusion criteria. COVID-19 was confirmed in 31.5% of HCWs receiving two doses of CoronaVac vaccine vs. 0.9% of HCWs receiving two doses of CoronaVac vaccine with mRNA booster (p < 0.001), and 9.8% of HCWs receiving two doses of ChAdOx1 vaccine vs. 1% among HCWs receiving two doses of ChAdOx1 vaccine with mRNA booster (p < 0.001). In the adjusted analyses, the estimated VE was 92.0% for two CoronaVac vaccines plus mRNA booster, and 60.2% for two ChAdOx1 vaccines plus mRNA booster, when compared to those with no mRNA booster. Of 246 samples screened for mutations, 191 (77.6%) were Delta variants. Conclusions While two doses of ChAdOx1 or CoronaVac vaccines prevent COVID-19, the addition of a Pfizer/BioNTech booster provided significantly more protection.

COVID-19 lateral flow IgG seropositivity and serum neutralising antibody responses after primary and booster vaccinations in Chile: a cross-sectional study

“…All studies concluded that homologous and heterologous booster doses significantly increase concentrations of different anti-SARS-CoV-2 antibodies (and sometimes cell-mediated immunity). 16 , 17 , 18 Studies comparing homologous versus heterologous booster responses among individuals receiving primary inactivated vaccines (mostly CoronaVac in China, Brazil, Turkey, and Thailand 19 , 20 , 21 , 22 ) report a more robust response with heterologous boosters. An antibody study from Brazil 23 and one effectiveness study from Chile 24 provided the most robust evidence for this conclusion.…”

Relative Vaccine Effectiveness of the Third Dose of CoronaVac or BNT162b2 Following a Two-Dose CoronaVac Regimen: A Prospective Observational Cohort Study from an Adult Vaccine Center in Turkey

“…In our study, unfortunately, the spike and non-neutralizing viral antibody levels of participants were not available. Nonetheless, the FDA does not advise antibody testing to evaluate immunity or protection from COVID-19, particularly among those who had vaccination [ 29 ]. Finally, our data exclude vaccine effectiveness against the Omicron variant and may not be generalized to the current status of the pandemic.…”

Comparative effectiveness of heterologous booster schedules with AZD1222, BNT162b2, or mRNA-1273 vaccines against COVID-19 during omicron predominance in the Nordic countries

“…Data to assess the effectiveness of heterologous booster schedules, however, are sparse and mainly limited to studies conducted during periods of delta variant predominance and/or as compared with unvaccinated. [10][11][12][13][14][15]17,18] To our knowledge, no study has reported the effectiveness of the individual heterologous booster schedules with the AZD, BNT, and MOD vaccines as compared with primary schedules during an omicron period. When compared with unvaccinated, heterologous and homologous schedules showed similar levels of improved protection against omicron infection [17] and severe COVID-19 [18].…”

“…Studies during delta predominance periods overall found improved protection of heterologous boosters compared with primary schedules, a protection that was comparable to the homologous boosters when indirectly compared. [10][11][12][13] However, the protection against severe COVID-19 was typically not analysed in these studies or the number of cases was very low precluding statistical precision.…”

“…[6][7][8][9] How these immunologic findings translate into effectiveness is less certain. [10][11][12][13][14][15][16] The use of heterologous booster strategies facilitates a more flexible approach for vaccination roll-out and simplifies logistics, but should be supported by evidence of effectiveness including protection against the omicron variant of concern. This evidence is currently lacking.…”