Cost effectiveness of fractional doses of COVID-19 vaccine boosters in India

Background: Coronavirus disease 2019 (COVID-19) continues to be a major global public health crisis that exacts significant human and economic costs. Booster vaccination of individuals can improve waning immunity and reduce the impact of community epidemics. Methods: Using an epidemiological model that incorporates population-level severe acute respiratory syndrome coronavirus 2 (SARS-CoV- 2) transmission and waning of vaccine-derived immunity, we identify the hypothetical potential ofmass vaccination with fractionated vaccine doses specific to ChAdOx1 nCoV-19 (AZD1222 [ Covishield]; AstraZeneca) as an optimal and cost-effective strategy in India's Omicron outbreak. Findings: We find that the optimal strategy is 1/8 fractional dosing under mild (Re similar to 1.2) and rapid (Re similar to 5) transmission scenarios, leading to an estimated $6 (95% confidence interval [CI]: -13, 26) billion and $2 (95% CI: -26, 30) billion in health- related net monetary benefit over 200 days, respectively. Rapid and broad use of fractional dosing for boosters, together with delivery costs divided by fractionation, could substantially gain more net monetary benefit by $11 (95% CI: -10, 33) and $2 (95% CI: -23, 28) billion, respectively, under the mild and rapid transmission scenarios. Conclusions: Mass vaccination with fractional doses of COVID-19 vaccines to boost immunity in a vaccinated population could be a costeffective strategy for mitigating the public health costs of resurgences caused by vaccine- evasive variants, and fractional dosing deserves further clinical and regulatory evaluation. Funding: Financial support was provided by the AIR@InnoHK Program from Innovation and Technology Commission of the Government of the Hong Kong Special Administrative Region.