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Pfizer has released preliminary data on its COVID-19 vaccine candidate. China News Service/Getty Images
  • A final analysis from Pfizer’s late-stage vaccine trial suggests the vaccine can prevent COVID-19.
  • This promising development comes as the United States reached another grim milestone of 11.4 million COVID-19 cases, with over 249,000 deaths.
  • The company plans to seek emergency use authorization from the FDA this month.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

Drugmaker Pfizer said on Wednesday that a final analysis of data from its late-stage coronavirus vaccine trial suggests that the vaccine can prevent COVID-19 in people who have not been exposed to the virus before.

This promising development comes as the United States reached another grim milestone of 11.4 million COVID-19 cases, with over 249,000 deaths.

Worldwide, more than 1.3 million people have died of COVID-19.

The Pfizer vaccine has been tested on over 43,000 people, with no serious safety concerns observed, the company said in a news release.

In the phase 3 trial, people were randomly assigned to receive two doses of the vaccine — 28 days apart — or an inactive placebo. Participants didn’t know which group they were in.

Seven days after the second dose, the vaccine had an effectiveness of 95 percent, the company reported.

This is higher than an early analysis released last week showing an effectiveness of better than 90 percent.

Dr. Sunil Sood, chair of pediatrics and an infectious disease specialist at Northwell Health’s Southside Hospital, said the results are very promising.

“This shows that most people who developed infection were placebo recipients,” he said, “and most of those who got the actual vaccine did not get infected.”

The company said it plans to seek emergency use authorization from the Food and Drug Administration (FDA) “within days.”

By then, researchers will have followed at least half of the participants for an average of 2 months after their second dose, as recommended by the FDA.

The company also said in its release that it expects to produce up to 50 million doses of the vaccine in 2020 and up to 1.3 billion doses in 2021.

Dr. Carlos Malvestutto, an infectious disease expert at The Ohio State University Wexner Medical Center, said the interim results of Pfizer’s trial are very encouraging.

“Obviously, 90 percent protection is the level of protection that we would love to have for all vaccines,” he said.

The effectiveness seen during the final analysis exceeds the 50 percent effectiveness target set by the FDA for coronavirus vaccines.

Ninety percent effectiveness is also similar to the protection provided by other viral vaccines, such as HPV, chicken pox, and measles.

Some researchers, though, told Healthline that not enough data has been released for them to comment on the results.

Pfizer, which developed the vaccine in collaboration with German biotech company BioNTech, released the results in a news release, not a peer-reviewed medical journal.

The final analysis is based on 170 confirmed cases of symptomatic SARS-CoV-2 infection. The company said 162 of those cases were in people who received the placebo, while eight were in the vaccine group.

Ten cases of severe COVID-19 occurred among study participants, with nine in the placebo group and one in the vaccine group.

No serious adverse events were observed among study volunteers who received the vaccine.

The only severe side effects were fatigue, which occurred in 3.8 percent of people after the first or second dose; and headache, which occurred in 2 percent of people after the second dose.

Older adults experienced fewer and milder side effects, the company said.

The results are promising, but many questions about the vaccine still need to be answered.

David Verhoeven, PhD, a researcher with the Nanovaccine Institute and an assistant professor of veterinary microbiology and preventive medicine at Iowa State University, said the level of protection seen during the interim analysis looks good, but it’s not clear how long it will last.

“We know from natural [SARS-CoV-2] infection that immunity may wane in 4 to 6 months,” he said. “[If this happens with the vaccine], you will likely need yearly booster shots.”

A recent study found that patients who had recovered from COVID-19 still had a strong cellular immune response 6 months after recovery, even after antibody levels had declined.

One of the researchers told The New York Times that this suggests immunity to the coronavirus could last for years.

Also unclear is whether the vaccine protects against severe disease, which increases the risk of dying from COVID-19.

“If researchers can show that people who are vaccinated and still get COVID-19 have milder disease, that would be a huge winner,” Malvestutto said.

For the analyses, researchers looked at whether the vaccine prevented symptomatic SARS-CoV-2 infection, which includes mild and moderate cases.

Pfizer included in its final analysis how many severe cases were in the placebo and vaccine groups, but didn’t indicate whether this difference was statistically significant.

Given the recent surge in COVID-19 cases in the United States, Malvestutto said researchers will likely see enough severe cases to know if the vaccine helps this group of people.

He said that we will also need longer-term data about the safety of the vaccine, even though Pfizer will meet the FDA’s minimum recommendations for assessing safety.

Researchers plan on following participants for 2 years after their second dose. The Centers for Disease Control and Prevention (CDC) also routinely monitors the safety of vaccines approved by the FDA.

Pfizer’s vaccine was not developed as part of Operation Warp Speed, the U.S. government’s coronavirus vaccine effort.

However, the Trump administration did agree in July to buy at least 100 million doses. Under this arrangement, people in the United States would receive the vaccine free of charge.

While Pfizer’s is the first vaccine to show promising results in a phase 3 trial, 10 other vaccines have reached this stage. These include a wide range of vaccine technologies.

Pfizer’s vaccine uses messenger RNA, or mRNA, to elicit an immune response in people who receive the vaccine. Moderna’s vaccine is also based on this technology.

Moderna released interim results from its phase 3 trial on Monday, showing that its vaccine is 94 percent effective.

This newer vaccine platform is being tested for use against other infectious diseases, such as seasonal flu, Zika virus, and rabies, but none have been approved for use in people.

Other technologies being used against the coronavirus include vaccines based on a DNA platform, weakened or inactivated versions of the virus, viral protein subunits, virus-like particles, or delivering a coronavirus protein using another virus.

Some of these technologies are new, while others have been around for years.

“With both old and new technologies being used, our chance of getting several successful vaccines is actually very high,” Sood said.

Given the size of the pandemic, multiple vaccines may be needed.

“We’ll need more than one vaccine that has good protection and is safe and well-tolerated,” Malvestutto said, “because that’s the only way we’re going to be able to really get control of this pandemic in a reasonable time.”

However, finding a safe and effective vaccine is just one hurdle that needs to be overcome.

Vaccines would still need to be manufactured and distributed. Pfizer’s and Moderna’s vaccines require ultra-cold storage, which adds another layer of complexity to distribution.

Persuading people to get vaccinated is another challenge.

An Axios-Ipsos survey from October found that only two-thirds of people in the United States said they would get a coronavirus vaccine if it had been approved by the FDA.

“You can have the most amazing vaccine,” Malvestutto said, “but if people don’t take it, then that’s obviously not going to help.”

One STAT-Harris poll, though, suggests that people may be more willing to be vaccinated if the vaccine has a higher efficacy.

But Sood said more work needs to be done to persuade people to get vaccinated, especially among hard-hit groups such as the Black and Latino communities.

“A lot of community action at the local grassroots level will be needed to explain the safety and efficacy of the vaccine, as well as the importance of getting this vaccine,” he said.