FILE - A doctor observes a blood clot expelled by a COVID-19 patient at Hospital General de Mexico on May 30, 2020 in Mexico City, Mexico. RELATED: Medical imaging shows the true scope of long-term effects caused by COVID-19AdvertisementThe NIH has entered into its third Phase 3 trial of the ACTIV-4 Antithrombotics master protocol for adaptive trials, which tests blood thinner treatments that could potentially help prevent any life-threatening blood clots in discharged adult patients, according to an NIH statement.This particular trial is part of the Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) initiative which is "a public-private partnership to develop a coordinated research strategy for prioritizing and speeding.