On Monday Nov. 9, pharmaceutical corporation Pfizer Inc. announced that early results from their tests for their COVID-19 vaccine showed that it is more than 90% effective at protecting people from the virus.
These results were received from an interim analysis of a study that included 43,538 volunteers, with 42% of participants coming from “diverse backgrounds.”
Each volunteer received two injections of Pfizer’s vaccine, approximately 21 days apart. Pfizer compared the number of COVID-19 cases among the participants who received the vaccine to a near-equal group of individuals who received an injection of a placebo vaccine.
In their Nov. 9 news release, Pfizer and its partner BioNTech revealed that, among the 94 cases of COVID-19 in their study group, results indicated that the vaccine would be over 90% effective in preventing the virus. For reference, the Food and Drug Administration (FDA) had previously stated that the minimum effectiveness rate for any COVID-19 vaccine would have to be 50%.
“I tend to be an optimist. I’ve been in vaccine development for over 35 years,” said Dr. William Gruber, senior vice president of vaccine clinical research and development at Pfizer. “But this is extraordinary, and I think it speaks well not only for the potential of this vaccine but potentially other vaccines that are out there in development for COVID-19.”
Shane Crotty, a professor at the Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology, shared similar sentiments.
“This result is towards the high end of expectations,” Crotty said. “Greater than 90% efficacy at preventing disease, with 94 COVID-19 cases to evaluate, is an excellent outcome. It would be good to see more of the data, but those are very convincing numbers.”
However, despite all this good news, there is more work to be done before Pfizer can ask the FDA for permission to distribute this vaccine. The FDA requires a minimum of two months of follow-up data from at least half of the volunteers of any study by a vaccine manufacturer, as “the most dangerous side effects from a vaccine occur within two months of getting the final injection,” according to the administration. Pfizer will have this data in the third week of November.
Natalie Dean, a biostatistician at the University of Florida, expressed cautious optimism at these results, but indicated that we need more information before moving forward in any substantial way.
“There remain many open questions, such as how well the vaccine is working across different age groups, how well it is preventing infection and severe disease,” Dean wrote in an email to National Public Radio (NPR) the day the results were released. “But for the pre-specified primary endpoint of laboratory confirmed symptomatic disease across the trial population, the numbers look very good.”
Pfizer’s trial is not intended to last for a specific period of time, as it is labeled as an “event-driven study,” which means it will continue and remain “incomplete” until the corporation records a total of 164 COVID-19 cases among its participant base.
Pfizer had planned to release four interim analyses throughout the duration of the study. Monday’s results came from the company’s second interim analysis.