New Pfizer vaccine appears 90 percent effective against COVID-19

The race to develop a COVID-19 vaccine entered its final sprint, this week. On November 9, early and very promising results were released from a trial of a leading candidate vaccine. The vacine appears to keep nine in 10 treated people from getting sick with the new coronavirus.

Pfizer and the German biotech company BioNTech co-developed the new vaccine. These companies shared their news in a press release. In it, they described preliminary results of their ongoing Phase III clinical trial. These tests are comparing infection risk in people who received the new vaccine against risks in those given a look-alike placebo (inactive agent).

The good news couldn’t come too soon. COVID-19 cases continue to soar globally. As of November 9, more than 50 million people have been infected worldwide. Of these, more than 1.2 million people have died. Some countries have announced new public lockdowns and other drastic measures to curb the infection’s spread.

“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,” said Albert Bourla in the release. He chairs Pfizer, a global drug company.

The data have not yet been peer reviewed by other scientists. In addition, the news release offers few details on the trial. But the group who received the new vaccine had only a tenth as many cases of COVID-19 as did people getting a placebo.

The trial has to date enrolled more than 43,000 people. Of those, 38,955 have completed the treatment regimen. It includes two injections spaced three weeks apart. By seven days after that second dose — a total of 94 people had come down with confirmed coronavirus infections.

The U.S. Food and Drug Administration recommends that to be effective, vaccinated people should get fewer than half as many cases of COVID-19 as the placebo group does. The new announcement suggests the new vaccine performed far better than that. However, this clinical trial is not over. Infection rates in the groups could change in the coming weeks or months.

Mark Slifka works at Oregon Health & Science University in Portland. As a viral immunologist, he studies how vaccines protect us from viruses. “It’s early, but we can be cautiously optimistic,” Slifka says. “Hitting greater than 90 percent [protection],” he says, is “where we want to see successful vaccines.”

The new drug is not quite ready for a U.S. rollout. To give it to the general public, the drug’s maker would have to apply for an “emergency use” authorization. In the United States, the Food and Drug Administration issues those. It requires some two months of data after volunteers have gotten their final doses to judge a vaccine’s safety. For Pfizer and BioNTech’s vaccine, that date is expected to come in the third week of this month.

The status of this and competing vaccines

An estimated 200 COVID-19 vaccines are in various stages of development. A few, including one from Cambridge, Mass.–based Moderna, Inc., also are expected to have data available soon on how well they work. Countries like China and Russia have approved other vaccines for limited use on segments of their populations. There are no data from final-stage (Phase III) trials yet for those COVID-19 vaccines. So it remains unknown how effective they may be. 

Indeed, Slifka notes, no one knows whether the efficacy of the Pfizer-BioNTech vaccine will hold up over time. “We just need to see if it maintains above, at or near that [90 percent] level. And if so, for how long.” And if its protectiveness falls a bit, he adds, “It just tells us when we would need to do another booster.”

Right now, the Pfizer group has not reported how many cases were recorded in each group. But the reported protection rate certainly suggests most who got sick were in the placebo group. Also still unknown is what share of the volunteers who got both vaccine doses were included in the new analysis. The companies had claimed they would conduct a preliminary analysis once 62 volunteers from the trial had come down with COVID-19.

Researchers plan to do a final analysis once 164 of the volunteers come down with COVID-19. The companies will then continue to follow the trial’s recruits for a total of two years.

The key to this vaccine

Making proteins is the job of nearly all cells. Most animals depend on DNA to store the genetic instructions used to make their proteins. Some viruses instead use RNA. The Pfizer and BioNTech vaccine contains what’s known as a viral mRNA. That’s a type of molecule that cells use to read the protein-making instructions.

Here, that mRNA holds the instructions to make a so-called spike protein. The virus uses that protein to bind to cells and enter them.

Nanoparticles encase the vaccine’s mRNA and deliver it to someone’s cells. Those cells then build replicas of the spike protein. In this way, the body learns to recognize that protein. Its immune system can later launch an assault against that protein when it encounters it in the future. That’s how this vaccine preps the body to deal with the coronavirus.

If a vaccinated person later encounters the virus for real, their body is ready to send in antibodies and other immune cells to fight the virus. The vaccine does not carry any infectious virus into the body. So it cannot infect cells.

Still, the vaccine does cause some mild to moderate symptoms. These may include pain at the injection site, fever and chills.

Does the vaccine prevent infection?

“These are certainly very promising results,” says Brianne Barker. She’s an immunologist at Drew University in Madison, N.J. But the news release does not mention if there was a difference in how sick the people were in each group, she notes. “That could be really important in terms of how this vaccine works in the population,” Barker says.

The news release also does not say the vaccine prevents infection. It only says that treated people didn’t get sick. That may simply mean they didn’t show symptoms (such as loss of smell, fever or trouble breathing). In fact, data have shown that many people, especially young people, can get infected but show no symptoms.

So, Barker cautions, “it’s possible that a vaccine could prevent disease but still allow you to get infected.”