The efficacy of vaccines in the context of SARS-CoV-2 and its variants: Role of Spatio-temporal boundary

The preference for a COVID-19 vaccine, among many available, may be difficult for common people and normally relies on efficacy values reported from clinical trials. Vaccine efficacy depends on statistical data from primary and secondary endpoints of a trial. This study provides a time-varying mathematical framework that compares two vaccines of contrasting efficacy (Pfizer-BioNTech and AstraZeneca-Oxford) using hypothetical trials with real-world data. Modeling shows that efficacies can fluctuate depending on the prevailing infection rate and demographics. The efficacy of AstraZeneca-Oxford can become comparable and even better than Pfizer-BioNTech, depending on the region and time of the clinical trials. We also introduce an idea of composite efficacy considering multi-variants and show that the efficacy of various vaccines shows differential sensitivity to the delta variant rampant in India.