The better-than-expected result is the first Phase III data from any of the four candidates now in the final stage of testing in the U.S.
“I can’t imagine better news on the vaccine front,” said Walid Gellad, director for the Center for Pharmaceutical Policy and Prescribing at the University of Pittsburgh. “Not only is it highly effective based on the press release, but there were 90 cases so we don’t have to deal with the skeptics about interim analyses, and there appeared to be no safety signals.”
Others noted that the information Pfizer had released was promising but still incomplete. “We should remain a little cautious, said Michael Head, a senior research fellow in global health at the University of Southampton in the U.K. “The provisional findings are made available in a press release, and the study is ongoing.”
President Donald Trump, who pushed unsuccessfully for a vaccine by Election Day, cheered the Pfizer result. “STOCK MARKET UP BIG, VACCINE COMING SOON. REPORT 90% EFFECTIVE. SUCH GREAT NEWS!” he wrote on Twitter.
More on the math: The data and safety monitoring board overseeing the Pfizer trial was able to calculate the vaccine’s effectiveness by comparing the number of Covid-19 cases among people who received the vaccine to those who got a placebo.
The higher the number of cases among the placebo group versus the experimental group, the more effective the vaccine. Pfizer has not released the breakdown of the initial 94 cases, but its trial blueprint said that 26 cases among the placebo group and 6 among the experimental group would indicate that the vaccine was 77 percent effective.
The initial data exceeded those expectations.
But: Pfizer is still collecting safety data to prove to the FDA that the vaccine is safe as well as effective. The agency wants vaccine developers to follow at least half of trial participants for two months after their final dose of vaccine or placebo, and track any side effects.
Supply and logistics challenges: Pfizer has said it can make up to 100 million doses by the end of the year — enough to vaccinate 50 million people — and possibly more than 1 billion by the end of 2021.
The U.S. government has already placed an initial order for 100 million doses of the vaccine at a cost of $1.95 billion and has an option to acquire another 500 million if the vaccine proves successful in Phase III trials.
The vaccine could be tricky to distribute if it secures emergency-use authorization. It must be stored at -94 degrees Fahrenheit, which requires special freezers or dry ice. The shot can only withstand normal refrigeration for up to 24 hours and room temperature for no more than two hours after thawing.
Pfizer said last week that it would forego the government’s vaccine distribution system because of those ultra-cold transport and storage challenges. Instead it has developed a fleet of temperature-controlled shippers it has developed that use dry use to keep the vaccine at the correct temperature.