Experts weigh in on Pfizer's COVID-19 vaccine

·6 min read

In long-awaited good news Monday, drugmaker Pfizer announced that its vaccine candidate — created with German biotechnology company BioNTech SE — was 90 percent effective in preventing COVID-19 in phase III clinical trials. The news, delivered via a press release, marks the first positive data to come from a late-stage COVID-19 vaccine trial.

Pfizer announced Monday that its COVID-19 vaccine, made with messenger RNA, has proven 90 percent effective in phase 3 clinical trials. (Photo: REUTERS/Dado Ruvic)
Pfizer announced Monday that its COVID-19 vaccine, made with messenger RNA, has proven 90 percent effective in phase III clinical trials. (Photo: Reuters/Dado Ruvic)

The phase III clinical trial involved approximately 44,000 participants from the U.S., Argentina, Brazil and Germany. Half of the participants were given a placebo; the other half a two-dose vaccine. In total, 94 individuals developed COVID-19, suggesting that, at 28 days, individuals given the vaccine were 90 percent immune to the virus.

With nearly 10 million cases of COVID-19 in the U.S. and more than 230,000 deaths, the news has been heavily praised by experts. In a statement released by Pfizer, the company chairman and CEO Dr. Albert Bourla called it a “great day for science and humanity,” suggesting that it brings the world one step closer to normalcy.

“We are reaching this critical milestone in our vaccine development program at a time when the world needs it most with infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen,” Bourla said. “With today’s news, we are a significant step closer to providing people around the world with a much-needed breakthrough to help bring an end to this global health crisis.”

As reactions to the news continue, here’s what you need to know.

Ninety percent efficacy is exceptionally high

Dr. Amesh Adalja, senior scholar at Johns Hopkins Center for Health Security, says the prevention level of the vaccine has come in much higher than vaccine experts and other scientists anticipated. “Most of us in the field did not think that these first-generation vaccines would provide anywhere near that level of efficacy of preventing infection,” Adalja tells Yahoo Life. “We thought their main value would be in preventing hospitalizations and deaths, but we were thinking of maybe 50 to 60 percent efficacy. So this is surprising.”

A 90 percent prevention rate is much higher than other common vaccines, including the influenza vaccine, which last year was 45 percent effective. The number also far surpasses the 50 percent efficacy that the Food and Drug Administration suggested as the cut-off for COVID-19 vaccine approval. But Dr. Gregory Poland, a renowned vaccinologist and head of the Mayo Clinic’s Vaccine Research Group who is on the review board for several COVID-19 vaccines (but not Pfizer’s), says mutations could influence the efficacy.

“We don't know anything about the efficacy of this vaccine against mutated viruses, and this is important,” Poland says. “These vaccines allow your body to see one piece of the virus. But what happens when that protein changes?”

The vaccine relies on messenger RNA, which has not been used in any previous vaccines

Pfizer’s vaccine, along with many of the 11 leading candidates, has been created with what’s known as “messenger RNA.” In 2015, Harvard researchers described this approach as a “novel technology” that could transform the vaccination world.

Poland explains how it works: “This is the genetic code for one piece of the virus, the spike protein. So you literally construct the genetic code and inject it into muscle cells, which uses our body's machinery to translate that series of nucleic acids into a protein,” he says. “That protein gets displayed on the outside of our immune surveillance cells, which see it, recognize it as a foreign and mount an immune response against it.

Moderna, another American drugmaker, has also created a vaccine that relies on mRNA, and experts say this new data may bode well for the company’s own candidate. “That’s another question we want to ask: Is this a class effect of mRNA?” Adalja says. “We haven't had an mRNA vaccine for humans but it does raise questions about whether the other vaccines like Moderna’s will have the same safety profile.”

The results came from an independent review board — but experts are urging Americans not to jump to conclusions

The analysis came from what’s known as an Independent Data Monitoring Committee, a group of scientists and other vaccine experts who are not affiliated with either Pfizer or BioNTech. Adalja says the research should be taken seriously but that more data is needed. “You just have to temper your enthusiasm because we want to see the full data in a peer-reviewed journal format in order to be able to completely determine what the efficacy level is and what the safety profile is,” he says. “Everybody is going to jump on the press release and I think it’s right to be enthusiastic but we need to be anticipating a full analysis.”

Poland says while it’s tempting to assume that the news means a vaccine is imminent, the results leave many critical questions unanswered. “This is encouraging but it’s a small sliver of results whose data we've actually not seen yet,” Poland says. “Vaccines require far more data over months to years.”

The 44,000 participants in the study, he says, are likely not representative enough to provide information on specific key groups, including those most vulnerable to the virus. “We know nothing about efficacy or safety in children, pregnant women, highly immunocompromised people, older people or the hardest-hit populations,” he says. “And you also have to remember, these are results for the most part in a world wearing masks. “What’s the efficacy when masks are off and we're not distancing? We don't know.”

No matter what, a vaccine will likely still not be available for the general public until 2021

Although the news is an exciting step forward, it doesn’t necessarily change the projected timeline of a vaccine. Pfizer will reportedly file for FDA approval in the next few weeks, but will still be required to prove that that vaccine is safe. In a statement released Monday morning, President-elect Joe Biden expressed optimism but reiterated that more steps are needed before a vaccine will be ready.

“This news follows a previously announced timeline by industry officials that forecast vaccine approval by late November,” Biden said. “Even if that is achieved, and some Americans are vaccinated by later this year, it will be many more months before there is widespread vaccination in this country.”

Adalja agrees. “I do think by the end of the year, health care workers may have access to a vaccine like this one under emergency use,” he says. “But this vaccination program is something that’s very likely to take well into 2021.”

Poland once again stresses that, despite the good news, we may be years away from fully understanding how well the vaccine works. “You don't know what you don't know,” he says. “Maybe a hundred thousand people have ever gotten one of these vaccines. We don’t know what the wider story will be.”

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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