ABSTRACT
Background: Limited Covid-19 vaccine effectiveness (VE) studies address the mRNA, adenoviral vector-based, and protein subunit vaccines and their mix and match in real-world settings. BNT162v2 (Pfizer-BioNTech), mRNA- 1273 (Moderna), AZD1222 (AstraZeneca), and locally produced MVC-COV1901 (Medigen) are provided under the National Vaccination Program. Taiwan maintained a low circulation of Covid-19 infection until a major epidemic Omicron BA.2, began in April 2022. The study aimed to estimate the VE against moderate and severe (severity) and fatal diseases (death) associated with SARS-CoV-2 among individuals administered one, two, and three doses of vaccination and categorized by vaccine type combinations in this predominantly infection-naive population. Method(s): The study included CDC's administrative records from National Immunization Information System and National Infectious Disease Reporting System from March 21, 2021, to September 30, 2022. Criteria for Covid-19 severity followed WHO's guidelines, and the committee reviewed the records. The study calculated each individual's last administered date to disease onset (incidence rate (IR) per 100,000 person-days) to explore the incidence rate to compare the presence of risk probabilities. Multiple logistic regression was used for vaccine effectiveness analysis. Result(s): Of 23,933,482 individuals included in the study, and 6,202,496 infections, 30,976 severity, and 10,851 deaths were observed. Compared with three doses administered, three doses of AZD1222 or it as primary series plus mRNA or protein-based vaccines were at higher risk of severity (IR: 0.390-0.762), followed by mRNA-1273 (IR: 0.316-0.471), MVC-COV1901 (IR: 0.044-0.196) and BNT162v2 (IR: 0.061-0.197). As for the death outcome, AZD1222 was at higher fatal risk (IR: 0.127-0.269), followed by mRNA-1273 (IR: 0.086-0.125), MVC-COV1901 (IR: 0.013-0.064) and BNT162v2 (IR: 0.015-0.045). VE against the severity of AZD1222 or it as primary series ranged from 65.9% to 77.7%;mRNA vaccines ranged from 86.4% to 96.1%;and protein-based vaccines ranged from 91.4% to 96.2%. A similar pattern of VE against death ranged from 60.9% to 73.7%, 88.2% to 96.2%, and 90.3% to 95.6%. Conclusion(s): Individuals who received their primary series as AZD1222 might not have adequate protection against Covid-19 severity so encourage those vulnerable groups to receive additional booster doses. The study also indicated that protein subunit vaccines provide similar protection against severity and death as mRNA vaccines. (Table Presented).