Trial landscape of fractional dosing studies of COVID-19 vaccines: a living review of evidence

June 2022 update: since this document has been last updated in February 2022, many new trials may have reported data. A recent meta-analysis paper (not yet peer reviewed as of this writing) by Yang et al. ( provides a systematic review of fractional dosing trials as of December 2021.

This is a living review of trials for fractional dosing of COVID-19 vaccines. To date, it includes 22 completed (19 with results available) and 20 ongoing trials (3 with results available), in addition to 2 studies in planning stage and a call for proposals. The table below does not represent a systematic review of studies. The evidence presented here derives from peer-reviewed papers, preprints, clinical trial registrations, press releases and direct communication with authors, prioritized according to the present order. The purpose of this revision is to map the efforts to test fractional dosing and the knowledge gaps that still must be addressed. This work builds on a paper by the same authors which revisits the existing evidence on fractional dosing and offers an epidemiological and economic analysis of potential impacts.

Więcek, W., Ahuja, A., Chaudhuri, E., Kremer, M., Simoes Gomes, A., Snyder, C. M., Tabarrok, A., and Tan, B. J. (2022), ‘Testing Fractional Doses of COVID-19 Vaccines’, Proceedings of the National Academies of Sciences forthcoming