COVID-19 Vaccine Trials Could Be Halted Early in Case of Overwhelmingly Positive of Negative Results, Says Anthony Fauci

The COVID-19 vaccine trials that are currently underway could end early if the results are found to be overwhelmingly positive or negative, according to top US infectious disease expert Dr. Anthony Fauci.

Scientists are presently testing three COVID-19 vaccines in large-scale US trials designed to enroll 30,000 participants each. However, researchers can come to know if their COVID-19 vaccine is effective after as few as 150 to 175 infections. In an interview with KHN, Fauci, director of the National Institute of Allergy and Infectious Diseases, said that although the ongoing clinical trials were likely to be completed by the year end, the Data and Safety Monitoring Board (DSMB) had the authority to end the trials weeks early if the interim results were overwhelmingly positive or negative. DSMB is an independent safety board and comprises experts in vaccine science and biostatistics who teach at major medical schools. DSMB periodically examines data from clinical trials to determine if it would be ethical to continue enrolling volunteers, who are randomly assigned an experimental vaccine or a placebo.


In case of overwhelmingly positive results, the DSMB could say, “The data is so good right now that you can say it’s safe and effective,’” Fauci said. Scientists then would have “a moral obligation” to end the trial early and make the COVID-19 vaccine available to all the study participants, including those who had been administered placebo shots, as well as speed up the process to deliver the vaccine to millions.

However, some scientists and health experts believe that stopping the trials due to adverse events would create fear over the safety of COVID-19 vaccines among the public. On the other hand, halting the trials due to positive data also posed safety risks as the smaller scale of the studies could fail to detect key side effects of the COVID-19 vaccine that would which would be visible only after millions of people had been vaccinated.

In a separate interview with MSNBC, Fauci said that based on the patient enrollment rate in the ongoing COVID-19 vaccine trials, enough clinical data would become available by November or December to know that one of the vaccines is safe and effective. “Is it conceivable that you could get an answer before then? Yes, it’s conceivable,” Fauci said. He also clarified that the US was not pursuing a strategy of “herd immunity.” “The fundamental strategy that we clearly articulate is to try to prevent as many infections as you possibly can prevent: identification, isolation, and contact tracing,” said Fauci.