Healthcare COVID-19 vaccine: Moderna says will begin Phase 3 trials with 30,000 participants in July Updated : June 12, 2020 05:58 PM IST Moderna has finalised the Phase 3 study protocol, which will include approximately 30,000 participants enrolled in the US to test its COVID-19 vaccine's effectiveness on a larger scale. The randomized, placebo-controlled trial is expected to begin in July. Subscribe to Moneycontrol PRO at just Rs.33/- per month for the first year. Use code SUPERPRO. Limited period offer. Available on Web and Android.