A UK study that is examining the effect of mixing different COVID-19 vaccines was expanded on Wednesday to include two more vaccines. The first round of the Comparing COVID-19 Vaccine Schedule Combinations (COM-COV) trial, which was launched in February, recruited 830 participants to trial combining the Oxford/AstraZeneca vaccine and the Pfizer/BioNTech vaccine. Now with the rollout of the Moderna vaccine beginning on April 7, and the Novavax vaccine expected to be approved soon, COM-COV2, the new trial launched on Wednesday, will add the two new vaccines into the mix. The study is expected to enroll 1,050 new participants aged 50 and over who have received only one dose of a COVID-19 vaccine (Pfizer or AstraZeneca) through the national immunisation programme between Jan. 25 and March 20. The participants will randomly receive either the same vaccine as their first dose, or a different one—Moderna or Novavax—without knowing which vaccines they received. The participants will be …