The two-dose adenovirus-vectored vaccine Ad26.COV2.S, which encodes the spike protein of SARS-CoV-2, is currently undergoing Phase III testing with the support of Johnson & Johnson. This randomized double-blind Phase III trial, known as ENSEMBLE 2, is enrolling up to 30,000 adult participants in multiple countries. The two doses are administered 56 days apart.

Johnson & Johnson has already announced interim efficacy results of the one-dose phase III ENSEMBLE trial of the same Ad26.COV2.S vaccine, finding an overall vaccine efficacy against laboratory-confirmed moderate to severe/critical COVID-19 of 66.1% across all geographic areas studied and as of at least 28 days after vaccination.

What will be the vaccine efficacy of the two-dose Johnson & Johnson Ad26.COV2.S vaccine candidate according to the results of Phase III testing?

In this study, as in the previous one-dose study, confirmed cases of COVID-19 are defined as molecularly confirmed moderate to severe/critical COVID-19, with cases only being considered as part of the efficacy analysis as of 14 days after the second dose. The overall vaccine efficacy figure for all geographic areas will be considered for resolution.

This question will close retroactively to the date when the interim results are released. However, it will not resolve on the basis of that efficacy data — rather, it will resolve on the basis of the final phase III efficacy data in a published peer-reviewed article.