An early glimpse at Pfizer’s experimental COVID-19 vaccine phase 3 clinical trial shows it to be both effective and safe so far, medical experts said Monday.
University Hospitals (UH) was chosen as one of 120 sites for the phase 3 trial in August. More than 43,000 people have been enrolled in the trial from all over the world, said Dr. Grace McComsey, vice president of research at UH.
Pfizer, one of many pharmaceutical companies participating in the worldwide race for a COVID-19 vaccine, announced in a press release that the vaccine appears to be more than 90 percent effective in preventing COVID-19 in participants.
To be considered for approval by the U.S. Food and Drug Administration (FDA), a vaccine has to have a minimum effectiveness rate of 50 percent.
“When you are above 90 [percent], even if it decreases a little bit in the final result, it still is going to be effective,” McComsey said. “The fact that we have that cushion between 90 [percent] and 50 [percent] is really good news. It’s amazing news, actually.”
During a phase 3 trial, researchers are evaluating how effective a drug or treatment is at preventing a disease using a large sample size. The Pfizer study is double-blind, meaning neither the participants nor researchers know whether a person was administered the vaccine or a placebo. Participants are diverse, McComsey said, and about 28 percent of participants in the final-stage Pfizer and BioNTech trial are minorities.
For the phase 3 trial’s preliminary analysis, researchers evaluated 94 cases of COVID-19 in participants, finding the vaccine was 90 percent effective in preventing COVID-19 infection, when compared to the placebo, McComsey said.
The study will not be finalized until 164 COVID-19 infections are analyzed, which the FDA said is statistically sufficient to tell whether the vaccine is working, she said.
Another key takeaway from Pfizer’s early analysis is that no serious safety concerns have been reported, McComsey said.
“For Pfizer to say, so far, no serious adverse events, is also huge, in terms of safety,” she said. “This is not a vaccine that has been put on hold before… it has not had any glitch in terms of safety.”
Dr. Thad Stappenbeck, department chair of inflammation and immunity at Cleveland Clinic’s Lerner Research institute, echoed McComsey’s excitement about the apparent high efficacy and safety of the experimental vaccine.
“The most exciting thing is that it’s safe,” he said. “They haven’t had any bad outcomes.”
Questions still remain about the vaccine’s length of immunity and whether it protects against severe infections, Stappenbeck said.
“We don’t know how long the level of immunity occurs. We don’t even have a great idea of that with natural infection,” he said. “I think that's something we will have to watch. So, will you need a booster in a year? That’s the kind of thing we don’t know yet.”
Some vaccines, such as the flu vaccine, can not only prevent an individual from contracting a disease, but can help prevent a severe case if someone is infected. It is not yet clear if any of the experimental COVID-19 vaccines have that capability thus far, Stappenbeck said.
“We still don’t totally understand susceptibility. It’s very possible then that this actually could reduce the severity, and that would be awesome, but again, we need data,” he said.
Pfizer is continuing to enroll participants for further vaccine research, and plans to apply for emergency use authorization of the vaccine in the third week of November, McComsey said.
By then, the trial participants evaluated in Pfizer’s interim analysis will have had at least two months of follow-up monitoring, she said, and researchers will have broader information about side effects or other safety issues.
If emergency authorization is approved, distribution will begin shortly, because the government has already paid for millions of doses to be manufactured, she said.
“At least a big chunk of them, per Pfizer, should be available at the end of this month,” McComsey said.
Front line health care workers will likely be the first ones to receive the vaccine, McComsey said. Military personnel and vulnerable populations, such as the elderly, are also a high priority, she said.
One of the reasons Pfizer is on track to come out with the first authorized vaccine is because the trial has had no delays, McComsey said. Other experimental vaccine trials, such as the phase 3 AstraZeneca trial, in which UH is also participating, have been paused due to safety concerns and illness in volunteers. Pauses in drug trials due to adverse events are common, though in the case of COVD-19 vaccine trials, such delays are getting more attention than usual.
A phase 3 COVID-19 vaccine trial being conducted by Moderna is also reporting favorable results, which means multiple different vaccines could be distributed at once, McComsey said, which is no different than other common vaccines, such as the flu shot, she said.
“We have several companies who manufacture flu shots – it’s not one,” McComsey said. “As long as they have efficacy and safety, whatever you see, you see. You don’t even ask which one.”
Different COVID-19 vaccines may be better suited for different people, she said. For example, the Moderna trial is studying populations with weakened immune systems, because the vaccine does not contain an actual virus and may be safer for immunocompromised individuals.
“If we discover that vaccine A is better for special populations, then that will be what that special population will take," she said. “If we discover a safety concern – let’s say that one of those vaccines, for example, is discovered that, in cancer, it may not be safe …we want to ensure that vaccine is not the one given to [cancer patients.] So that will be refined after.”
The vaccine being tested in the Pfizer trial was developed using mRNA proteins, which carry genetic material that tell the body to make antigens that mirror the SARS-COV-2 virus, building up immunity. As with the Moderna vaccine trial, no live virus is being injected into participants, McComsey said.
Pfizer trial participants received two doses of the vaccine, three weeks apart, she said.
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