An independent panel of experts has overwhelmingly voted to recommend that the Food and Drug Administration authorize Pfizer's Covid-19 vaccine for emergency use in people ages 16 and older.
The vote Thursday afternoon was 17 in favor of the authorization and four against, with one person abstaining.
The members of the Vaccines and Related Biological Products Advisory Committee, or VRBPAC, were not given an opportunity to explain their votes against recommending authorization. However, there was much discussion before the final vote to recommend authorizing the shots for teenagers 16 and 17 years old. Some experts worried there was not enough data to make an informed decision about the vaccine in adolescents.
One of the members who voted no, Dr. David Kim, director of the vaccines division of the Office of Infectious Disease and HIV/AIDS Policy in the Department of Health and Human Services, told CNBC in an email that he would have voted yes "most enthusiastically" had the vote been limited to recommending authorization to those ages 18 and older.
Although the FDA is not obligated to go along with the panel's recommendation, it is widely expected to authorize the vaccine for emergency use promptly.
"Our plan is to take their recommendations into account for our decision-making and make a decision shortly thereafter," the FDA's commissioner, Dr. Stephen Hahn, said Thursday on NBC's "TODAY" show. "It really depends upon the complexity of the issues discussed, but we intend to act quickly."
The United States would be the fourth country to move forward with Pfizer's vaccine. Canada approved the vaccine Wednesday, and the United Kingdom began administering the shots this week. Bahrain has also granted access to the vaccine.
Data so far indicate that the vaccine is safe and 95 percent effective across a variety of age and racial groups and ethnicities when given in two doses, about three weeks apart.
Outside experts have been unusually effusive with praise for Pfizer's vaccine work.
"The trial results are impressive enough to hold up in any conceivable analysis," Dr. Eric Rubin, an immunologist at the Harvard T.H. Chan School of Public Health, wrote in an editorial published Thursday in the New England Journal of Medicine, where he is editor-in-chief.
"Most vaccines have taken decades to develop, but this one is likely to move from conception to large-scale implementation within a year," he wrote. "This is a triumph."
While Thursday's vote is seen as a positive step toward combating the pandemic, it comes as the number of people who dying of Covid-19 is increasing alarmingly. On Wednesday, the number reached a new high, surpassing 3,000 deaths in a single day, according to an NBC News tally.
The shots are known to come with some side effects, including fever, fatigue, headache and muscle and joint pain. Two people in the U.K. were reported to have had severe allergic reactions after getting the shot.
Dr. Paul Offit, a VRBPAC member and vaccine researcher at the Children's Hospital of Philadelphia, urged continued studies to learn more about the potential for allergic reactions to the vaccine and to reassure those who have severe allergies in general.
The matter needs "careful observation to prove that this is not going to be a problem," Offit said. "You've got tens of millions of people who are not going to get this vaccine because of the comments that were made" by health officials in the U.K.
"We need to offer people some solace," he said. "This issue is not going to die until we have better data."
Such reactions are partly why clinical trials of Pfizer's vaccine will continue. Its safety and effectiveness will also continue to be scrutinized, even after shots start going into arms.
During Thursday's meeting, Dr. Nancy Messonnier, director for the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention and head of the agency's work on Covid-19 vaccines, outlined the various tracking platforms and databases that will watch for any potential adverse events or problems that could be related to the vaccine.
"On day one of the Covid-19 vaccine program, systems will be in place to monitor the safety of vaccine recipients," she said. The systems will include tried-and-true monitoring databases, such as the Vaccine Adverse Event Reporting System, as well as a new CDC database called V-SAFE, which uses text messaging and online surveys to check in with people who have been vaccinated to identify potential safety issues.
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Another consideration is one of ethics: Should those who participated in clinical trials but received the placebo be offered the real vaccine?
Pfizer has said those participants should be offered the vaccine, but many purists of the scientific process urge the trials to continue as is to collect as much safety and efficacy data as possible.
What's more, experts say, additional information about the vaccine's effects on pregnant women, young children and those who are severely immunocompromised will be needed.
The advisory panel is scheduled to meet again virtually Dec. 17 to consider a similar vaccine, made by Moderna. In November, the company released preliminary results from its Phase 3 trial, which showed that the vaccine is nearly 95 percent at preventing symptomatic illness.
More details from Moderna are expected to be released publicly before next week's meeting.
Elsewhere in the pipeline, vaccine candidates from AstraZeneca and Johnson & Johnson are continuing with Phase 3 trials, with results likely after the New Year.