Science’s COVID-19 reporting is supported by the Pulitzer Center and the Heising-Simons Foundation.
The preliminary report 1 month ago that an experimental COVID-19 vaccine made by Pfizer and its partner BioNTech had 95% efficacy startled the world. But few surprises occurred today when the vaccine advisory committee to the U.S. Food and Drug Administration (FDA) strongly backed the companies’ request for an emergency use authorization (EUA) of their candidate for people 16 years of age and older. If FDA promptly accepts the recommendation, as is expected in the next few days, select groups of people in the United States could, for the first time, begin to receive COVID-19 vaccines outside of a clinical trial.
Other scientists hailed the panel’s decision. “It’s great to know that we have efficacious products coming online and will soon be available to folks,” says Natalie Dean, a biostatistician who specializes in vaccines at the University of Florida. The vaccine’s level of efficacy, she says, “exceeded expectations.”
The panel’s much-anticipated vote comes several days after the United Kingdom began to vaccinate the elderly and front-line health care workers with the Pfizer-BioNTech vaccine, which the country authorized for emergency use on 2 December. The vaccine, developed using an innovative strategy never used in the United States outside of clinical trials, contains messenger RNA (mRNA) that codes for the surface protein, spike, of SARS-CoV-2, the pandemic virus.
As Pfizer scientists explained to the Vaccines and Related Biological Products Advisory Committee (VRBPAC) today, the mRNA preparation powerfully prevented symptomatic cases of COVID-19 in an efficacy trial involving about 44,000 volunteers: Only eight people who got two shots of the vaccine spaced 21 days apart developed the disease, as compared with 162 participants in the placebo group, an efficacy of 95%. Severe disease occurred in nine placebo recipients, but only in one vaccinee—and that one person had a temporary low oxygen level and wasn’t hospitalized.
After hearing detailed presentations about the vaccine’s efficacy and safety data from Pfizer and FDA scientists, as well as public comments, the VRBPAC voted 17 to four in favor of the EUA with one abstention. Several members who did not vote for the EUA stressed that they only objected to allowing the vaccine’s use in 16- and 17-year-olds, because few were in the study and scant safety data exist for those ages. “Adolescents do not get very sick [from COVID-19], seldom get hospitalized, and I’ll bet it’s a very small number of deaths,” said Cody Meissner, a pediatrician at Tufts University School of Medicine, who didn’t think the risk for that age bracket was worth the potential benefit.
Although the vaccine clearly required both doses to offer the most robust protection, the Pfizer scientists noted that protection began to appear about 2 weeks after the first dose. An analysis of symptomatic COVID-19 that occurred between dose one and two found 32 cases in the vaccinees versus 82 in the placebo recipients, which translates to an efficacy of 52.4%. Neither FDA staffers nor Pfizer representatives advocated using just a single dose, as two doses clearly offered far more robust protection. But the early evidence of efficacy indicates that the vaccine could start to have an impact about 1 month before it reaches its peak powers.
The trial studied the vaccine in participants who ranged from ages 12 to 91. SARS-CoV-2 causes the most severe disease and death in the elderly and in people who are obese or have underlying comorbidities like diabetes or chronic respiratory problems. Those over age 65 made up 21% of the total participants in the trial. Black people, who also suffer disproportionately from COVID-19, made up about 10% of the volunteers. More than one-third of the volunteers were obese, and one in five had a comorbidity. Most of the participants live in the United States, but trial sites were also in Argentina, Brazil, Germany, South Africa, and Turkey.
Some VRBPAC members raised concerns about the limited amount of safety and efficacy evidence in Black people, Native Americans, and the elderly. Other shortcomings highlighted during the 6-hour virtual meeting included the dearth of data that show vaccination prevents severe disease, no evidence that vaccination prevents transmission, and unknowns about the safety and efficacy in pregnant women (they were excluded from joining the study) and their babies. There were worries, too, about rare side effects that have surfaced—but aren’t clearly linked to the vaccine—including Bell’s palsy (in which facial muscles are disabled, causing cheeks and lips to droop), and anaphylaxis, which two people receiving the vaccine this week in the United Kingdom developed.
But several members of the committee, which is mainly made up of medical doctors, stressed that the vaccine’s benefits clearly outweighed the risks. “I think the safety is pretty well demonstrated and, balanced against over 2500 deaths a day,” an EUA makes sense, Meissner said.
One of the thornier questions FDA asked the committee to weigh in on was not put to a vote, but led to much discussion and debate: Should trial participants who received the placebo now be offered the mRNA vaccine? Pfizer contends that if FDA issues an EUA, trial participants who choose to leave the study will need to know whether they received placebo or vaccine. Company officials asked FDA to allow them to vaccinate placebo recipients if they would qualify for it outside of the study; basically, because of predicted shortages of the hard to produce vaccine for the next few months, prioritization schemes will determine who moves to the front of the line for the first doses. Offering placebo recipients the vaccine, Pfizer contends, could allow the company to keep following them and add more data to the study.
Steven Goodman, an epidemiologist at Stanford University who gave the panel a presentation about clinical trial bioethics, said the Pfizer study did not promise all participants they would receive the vaccine early for participating. “I don’t think we have that special obligation to give them the vaccine immediately,” Goodman said, arguing that placebo recipients should not be “jumping the queue” ahead of people who were at greater risk or need of vaccination.
Goodman proposed an alternative scheme. Trial participants would not be told whether they received placebo or vaccine, in part to make sure that behaviors that risk people’s exposure to SARS-CoV-2 remain the same in each group. Then, when trial participants become eligible for vaccination based on their local or a federal prioritization scheme, they would get shots—vaccines if they were in the placebo group and placebos if they already were immunized. That way, the knowledge of vaccine status, and therefore risk behaviors, would remain constant throughout the study. “This would give [participants] an avenue to stay within the trial,” said Goodman, who noted most people join vaccine studies for altruistic reasons. “If they didn’t want to wait for their allocation to become available through their eligibility locally, withdrawing wouldn’t get them the vaccine any earlier. So, there’d be no motivation to withdraw.” Still, the issue ultimately will be settled between FDA and Pfizer; the panel did not even weigh in with an unofficial vote.
FDA stressed that an EUA is not an approval but a temporary stopgap during an emergency. Pfizer said it expected to have enough efficacy and safety data to seek a full approval by April 2021. Animal studies that may shed light on risks to pregnant women and their babies may also provide data this month, and some information may come from women who became pregnant during the ongoing study.
Peter Marks, who heads FDA’s vaccine division, thanked everyone who took part in the meeting. “Having this as a transparent process is very important as one of the steps we are taking to try to enhance vaccine confidence across the country,” Marks said.
FDA has received intense criticism for, in the face of intense pressure from President Donald Trump and his administration, earlier issuing EUAs for COVID-19 treatments, including hydroxychloroquine, that had little, if any, compelling evidence to back their use and no input from advisory committees. The Pfizer-BioNTech COVID-19 meeting today provided a sharp contrast both in the compelling argument for an EUA and the open discussions.
“It was a great effort by our career scientists who maintained the high scientific standards that the world has come to expect of the FDA,” Marks told ScienceInsider after the meeting. “And it now brings us to the brink of the next step that will allow us to begin to actively work to overcome the pandemic in the United States through vaccination.” He says his team needs “a few days” to make a decision and will “work as quickly as possible.”
Ruth Karron, who runs the Center for Immunization Research at Johns Hopkins University’s Bloomberg School of Public Health, says it’s remarkable that science moved from the viral sequence to a highly effective, working vaccine in less than 1 year. “Now we have to ensure that this vaccine—and the highly effective vaccines that will likely follow—are administered efficiently and equitably, and that people are ready and willing to receive them,” she says.