Pfizer Vaccine Data Show 90% Efficacy in Early Results

Doug Brunk

November 09, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

A vaccine candidate against SARS-CoV-2 has been found to be 90% effective in preventing COVID-19 in trial volunteers who were without evidence of prior infection of the virus, results from an interim analysis of a phase 3 study demonstrated.

BTN162b2, a messenger RNA–based vaccine candidate that requires two doses, is being developed by Pfizer and BioNTech SE independently of the Trump administration's Operation Warp Speed. A global phase 3 clinical trial of BTN162b2 began on July 27 and has enrolled 43,538 participants to date; 42% of enrollees have racially and ethnically diverse backgrounds.

According to a press release issued by the two companies, 38,955 trial volunteers had received a second dose of either vaccine or placebo as of November 8. An interim analysis of 94 individuals conducted by an independent data monitoring committee (DMC) found that the vaccine efficacy rate was above 90% 7 days after the second dose. This means that protection was achieved 28 days after the first vaccine dose.

"It's promising in that it validates the genetic strategy — whether it's mRNA vaccines or DNA vaccines," Paul A. Offit, MD, told Medscape Medical News. Offit is a member of the US Food and Drug Administraiton's (FDA's) COVID-19 Vaccine Advisory Committee. "All of them have the same approach, which is that they introduce the gene that codes for the coronavirus spike protein into the cell. Your cell makes the spike protein, and your immune system makes antibodies to the spike protein. At least in these preliminary data, which involved 94 people getting sick, it looks like it's effective. That's good. We knew that it seemed to work in experimental animals, but you never know until you put it into people."

According to Pfizer and BioNTech SE, a final data analysis is planned once 164 confirmed COVID-19 cases have accrued. So far, the DMC has not reported any serious safety concerns. It recommends that the study continue to collect safety and efficacy data as planned. The companies plan to apply to the FDA for emergency use authorization soon after the required safety milestone is achieved.

Pfizer CEO Albert Bourla, DVM, PhD, added in a separate press release, "It's important to note that we cannot apply for FDA Emergency Use Authorization based on these efficacy results alone. More data on safety is also needed, and we are continuing to accumulate that safety data as part of our ongoing clinical study.

"We estimate that a median of two months of safety data following the second and final dose of the vaccine candidate ― required by FDA's guidance for potential Emergency Use Authorization ― will be available by the third week of November."

Offit, professor of pediatrics in the Division of Infectious Diseases at the Children's Hospital of Philadelphia, in Pennsylvania, said that if BTN162b2 is approved, administering it will be tricky. "This particular vaccine has to be shipped and stored at –70° C or –80° C, which we've never done before in this country," he said. "That means maintaining the product on dry ice. That's going to be a challenge for distribution, I think."

Good News, But…

In the press release, BioNTech SE's cofounder and CEO, Ugur Sahin, MD, characterized the findings as "a victory for innovation, science and a global collaborative effort. When we embarked on this journey 10 months ago this is what we aspired to achieve. Especially today, while we are all in the midst of a second wave and many of us in lockdown, we appreciate even more how important this milestone is on our path towards ending this pandemic and for all of us to regain a sense of normality."

President-elect Joe Biden also weighed in, calling the results "excellent news" in a news release.

"At the same time, it is also important to understand that the end of the battle against COVID-19 is still months away," he said. "This news follows a previously announced timeline by industry officials that forecast vaccine approval by late November. Even if that is achieved, and some Americans are vaccinated later this year, it will be many more months before there is widespread vaccination in this country.

"Today's news does not change this urgent reality. Americans will have to rely on masking, distancing, contact tracing, hand washing, and other measures to keep themselves safe well into next year," Biden added.

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