The vaccine Isabella would test is produced by the pharmaceutical companies Pfizer and BioNTech and relies on a new technology: messenger RNA, or mRNA (see How an mRNA Covid-19 Vaccine Works). Scientists have been studying mRNA technology for more than 30 years. When Covid-19 started to spread, companies realized that mRNA could be used to rapidly produce a vaccine against SARS-CoV-2, the virus that causes Covid-19.
To make sure a new treatment is safe and effective, companies carry out a series of clinical trials, or research studies that involve people. Each trial has three phases. Phase I tests the new treatment for safety on a small number of people. Phase II involves several hundred people and tests how well the vaccine works. Phase III, the final and largest phase, includes thousands of participants. The large sample size allows researchers to assess how effective a treatment is.
More than 44,000 adults participated in Phase III of Pfizer- BioNTech’s trial, which showed that the vaccine was 95 percent effective at preventing people from becoming ill with Covid-19. Once the new vaccine was deemed safe in adults, Pfizer-BioNTech expanded testing to more than 2,200 teens and preteens.