The news — out Oct. 27 — comes after the company’s CEO Albert Bourla had repeatedly hinted that such data would be available by October.
An independent data monitoring committee has a threshold for when to perform such an analysis: when 32 trial participants from a pool of 42,000 are infected with COVID-19. A positive result would be if 26 or more participants of those 32 infected patients had received a placebo in the trial. The study will continue until 150 participants are infected with the virus.
Analysts are divided on how to interpret the lack of an interim analysis.
The fact that Pfizer has yet to conduct an interim analysis is a “good thing,” according to Umer Raffat, a senior managing director at investment bank Evercore ISI cited in Stat News. Raffat reasoned that the state of affairs indicates that the BNT162 mRNA-based vaccine candidate had thus far not failed in preventing more than 77% of COVID-19 cases.
But the lack of an interim analysis could also signal that clinical trial participants are less likely to report novel coronavirus infections than the U.S. population at large.
Another cause could be a slower-than-anticipated COVID-19 infection rate. In September, Pfizer and partner BioNTech announced a proposal to expand their Phase 3 study from approximately 30,000 to 44,000 participants. Ugur Sahin, CEO of BioNTech, stated at the UBS COVID-19 Vaccine Symposium that part of the justification for the expansion was a slower-than-anticipated COVID-19 infection rate.
Pfizer’s press release on the vaccine candidate trial expansion stressed its potential to improve the diversity of the trial population.
Other possible reasons for the lack of an interim analysis include a lower-than-expected symptomatic rate for COVID-19, according to research from UBS. The firm had assumed 60% of those exposed develop symptoms, but it more recently assumed that the symptomatic rate could be as low as 30%. CDC has considered the possibility that the asymptomatic rate is as low as 10% and as high as 70%.
“Our CEO, Albert Bourla, has said before we are moving at the speed of science and we may have a readout by the end of October,” said company spokesperson Jerica Pitts. “Pfizer is working tirelessly to develop and produce, in record time, a safe and effective vaccine in the fight against COVID-19. We understand that time is of the essence to bring to market health solutions that help mitigate this pandemic, so we are working as fast as possible without cutting corners. Our pivotal clinical trial is event-based, so read-out timing ultimately will be driven by several fluid factors, including infection rates.”
Signs are building that FDA officials are fearful of the prospect of approving COVID-19 vaccines before thoroughly vetting them. On Oct. 6, FDA issued new guidelines on criteria for emergency use authorization for COVID-19 vaccines.
“We are committed to expediting the development of COVID-19 vaccines, but not at the expense of sound science and decision making,” wrote FDA Commissioner Stephen M. Hahn and Peter Marks, the director of FDA’s Center for Biologics Evaluation and Research on FDA’s website. “We will not jeopardize the public’s trust in our science-based, independent review of these or any vaccines. There’s too much at stake.”