In an unusual move, on March 23, the U.S. National Institute of Allergy and Infectious Diseases (NIAID) issued a strongly worded statement asking AstraZeneca to “ensure the most accurate, up-to-date efficacy data be made public as quickly as possible. On March 22, AstraZeneca released the results of the long-awaited U.S. trial of its COVID-19 vaccine, developed with scientists from Oxford University’s Jenner Institute.
The data showed that the two-dose vaccine was 79% efficacious in protecting people from symptoms of COVID-19 and 100% productive in protecting against severe disease. That data, however, may not have included the most updated information that the independent Data Safety Monitoring Board (DSMB), which reviews U.S. vaccine studies, had shared with the company. U.S. trials of COVID-19 vaccines are conducted under randomized, double-blind conditions, which means neither the doctors and staff running the trials nor the participants volunteering to know whether they are receiving the actual vaccine being tested or a placebo.
Only the DSMB has the authority to unblind the data to determine both efficacy and reveal any safety concerns. The DSMB does periodic unblinding checks to see, for example, if side effects are occurring at higher rates in the vaccinated versus placebo groups. The DSMB also determines if enough cases of COVID-19 have accumulated to provide the statistical power necessary to determine whether a vaccine works.