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Pfizer-BioNTech's COVID-19 results missing crucial details on vaccine's efficacy

Results from Pfizer Inc. and BioNTech SE's coronavirus vaccine were met with plenty of anticipation and strong market reactions, but industry experts urged caution until the final data arrives.

Interim results from the late-stage trial showed the vaccine achieved more than 90% efficacy, although the companies have yet to publish a detailed analysis, which is expected to provide further clarity about the inoculation's ability to prevent infection.

Positive final results could see the vaccine candidate, an mRNA-based shot called BNT162b2, gain emergency use authorization from the U.S. Food and Drug Administration as early as December, Mizuho analyst Vamil Divan told S&P Global Market Intelligence in an interview. Full approval will require an advisory committee meeting and further scrutiny of the data.

The study will continue until 164 cases of COVID-19 are reported among participants, but the high efficacy in the interim analysis puts the trial in a good position to pass the FDA threshold, Divan said.

"You're going to get some variability, but the likelihood of it dropping all the way to the 60% range ... is very unlikely," Divan said. "And that is why with these interim analyses they usually have a higher bar."

Several questions remain ahead of the full results, however, including a breakdown of demographics and disease severity, Divan added.

Epidemiologist Michael Osterholm, a newly named member of President-elect Joe Biden's COVID-19 advisory board, said the interim results were not enough to support concrete conclusions.

"What they haven’t done is said what percentage of those were just mild illnesses, and what percentage of those were severe illnesses," Osterholm said in a Nov. 9 radio interview with WCCO News Talk 830. "We’re hopeful that the Pfizer data for coronavirus will say we’ve prevented 90% of severe infections, hospitalizations, death — and if we don’t have that number there, then preventing 90% of muscle ache, fever and chills is a very different kind of outcome."

Final efficacy expected to be lower

A group of biostatisticians and clinical trial investigators all expect the final efficacy percentage to drop from 90%, according to information gathered by GlobalData pharma writer Reynald Castañeda.

This decrease in efficacy could be caused by a change in demographics as the number of trial participants with COVID-19 rises from 92 to 164, Castañeda told S&P Global Market Intelligence in an interview. As the interim results were measured seven days after the second shot, another possibility is that the vaccine's effectiveness wanes over time.

"The longer you follow people after the booster shot, there's the potential for the vaccine efficacy to go down," Castañeda said. "But for the efficacy to go all the way down to 50% in the final analysis is highly unlikely."

Castañeda said the chances of the FDA not granting emergency use are also very low since the regulator's threshold of 50% was far exceeded in the interim results, but a drastic drop in efficacy would cause concern.

"If efficacy goes all the way down to 50%, it's [still] approvable," Castañeda said. "But if it did go all the way down there from 90%, that's when people are going to be looking for a red flag somewhere."

Vaccine trials in the past have sometimes run for decades before accumulating enough data to show high efficacy, so with the speed of coronavirus vaccine trials that only began in March, it is difficult to find a precedent to help make accurate predictions about the final outcome.

Vaccine race continues

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Pfizer and Germany's BioNTech have agreed to supply 300 million doses to the U.S. in 2021, along with millions more around the world.

Meanwhile, Moderna Inc. is expected to release results for its own mRNA vaccine candidate soon, which will draw comparisons to Pfizer and BioNTech's shot. The efficacy rates will be important down the road as the companies compete, especially if there are stark differences, Divan said.

"If one vaccine falls 20% or 30% below another one, then that could change things," Divan said. "But to put up a pretty good data set here that holds up, it does kind of raise the bar a little bit on what the other companies need to show."

Castañeda said comparing vaccines can be hard because of the many nuances in a clinical trial, such as the time spent evaluating patients after inoculation and the number of shots involved.

But Pfizer has set the scene for how effective coronavirus vaccines can be, Castañeda said.

"The 90% efficacy really struck a chord with the public with regards to where the pandemic is going," Castañeda said. "There's a risk if companies like Moderna or Johnson & Johnson report something like 70% efficacy even with more specific data, it could be received as less efficacious even if it is an advantage."

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