Johnson & Johnson (J&J) has begun the second part of its global phase 3 trial evaluating COVID-19 vaccine candidate JNJ-78436735.

The study, conducted in partnership with the UK’s National Institute for Health Research, will enroll up to 30,000 participants to assess whether a second dose of the vaccine leads to greater efficacy. The first part of the study, also enrolling 30,000 participants, is testing whether a single-dose regimen is effective.

Interim data from an early-stage trial indicated JNJ-78436735 delivered an immune response and was well-tolerated, J&J said.