Background: The world is dealing with both the declining vaccine effectiveness and increasing demand for booster doses to address SARS-CoV-2 virus mutations. This study explore various vaccination strategies to model reduce illness and determine those approaches that are cost-effective.

Methods: We established a transmission-dynamic-model to predict the spread of SARS-CoV-2 infection within 6 month period under three strategies: discontinuing vaccination; prioritizing second shot; and prioritizing booster dose. Outcomes of interest included infected cases, deaths, quality adjusted life days (QALDs). We considered the impact of social factors in the scenario analysis, and also included uncertain assumptions and parameters in the sensitivity analysis.

Findings: The number of avoided cases/severe cases with prioritizing second shot and prioritizing booster dose was 462/88 and 585/61 compared with discontinuing vaccination (2357/269) within 180 days. Prioritizing booster vaccination could potentially save 895∙71 QALYs and USD −$12,564∙19. The scenario analysis indicated that prioritizing second shot may become more effective and beneficial with increased mask-wearing rate and nucleic acid tests requirement.

Interpretation: When both rates of quarantine and mask-wearing were relatively high, prioritizing booster vaccination was less costly and could avoid more infections. However, prioritizing second shot could avoid more cases of critically-ill and could override the latter under stricter epidemic control, indicating that booster vaccination has great limitations in improving the protective effect against SARS-CoV-2 mutation. This study provides evidence for effectiveness and cost-effectiveness regarding whether and how to provide vaccine shots and also confirms that strict epidemic controls remain valuable in countries with insufficient vaccine supply.

Keywords: COVID-19 vaccines, vaccination priority, dynamic transmission model