WASHINGTON — The coronavirus vaccine made by Pfizer and BioNTech provides strong protection against Covid-19 within about 10 days of the first dose, according to documents published on Tuesday by the Food and Drug Administration before a meeting of its vaccine advisory group.
The finding is one of several significant new results featured in the briefing materials, which include more than 100 pages of data analyses from the agency and from Pfizer. Last month, Pfizer and BioNTech announced that their two-dose vaccine had an efficacy rate of 95 percent after two doses administered three weeks apart. The new analyses show that the protection starts kicking in far earlier.
What’s more, the vaccine worked well regardless of a volunteer’s race, weight or age. While the trial did not find any serious adverse events caused by the vaccine, many participants did experience aches, fevers and other side effects.
“This is what an A+ report card looks like for a vaccine,” said Akiko Iwasaki, an immunologist at Yale University.
On Thursday, F.D.A.’s vaccine advisory panel will discuss these materials in advance of a vote on whether to recommend authorization of Pfizer and BioNTech’s vaccine.
Pfizer and BioNTech began a large-scale clinical trial in July, recruiting 44,000 people in the United States, Brazil and Argentina. Half of the volunteers got the vaccine, and half got the placebo.
New coronavirus cases quickly tapered off in the vaccinated group of volunteers about 10 days after the first dose, according to one graph in the briefing materials. In the placebo group, cases kept steadily increasing.
The vaccine’s swift impact could benefit not just the people who get it but the country’s strained hospitals, curbing the flow of new patients into intensive care units.
Despite the early protection afforded by the first dose, it’s unclear how long that protection would last on its own, underscoring the importance of the second dose. Previous studies have found that the second dose of the Pfizer-BioNTech vaccine gives the immune system a major, long-term boost, an effect seen in many other vaccines.
The efficacy of the vaccine after the first dose is about 52 percent, according to Dr. William C. Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development. After the second dose, that rises to about 95 percent. “Two doses of vaccine provide maximum protection,” he said.
Many experts have expressed concern that the coronavirus vaccines might protect some people better than others. But the results in the briefing materials indicate no such problem. The vaccine has a high efficacy rate in both men and women, as well as similar rates in white, Black and Latino people. It also worked well in obese people, who carry a greater risk of getting sick with Covid-19.
Some vaccines for other diseases set off a weak immune response in older adults. But Pfizer and BioNTech found that people over 65 got about as much protection from the coronavirus vaccine as younger people did.
Even if the vaccine is authorized by the F.D.A., the trial will continue. In the briefing documents, the companies said that they would encourage people to stay in the trial as long as possible, not knowing whether they got the vaccine or the placebo, so that the researchers could continue to collect information about whether the vaccine was safe and effective.
Confused by the all technical terms used to describe how vaccines work and are investigated? Let us help:
- Adverse event: A health problem that crops up in volunteers in a clinical trial of a vaccine or a drug. An adverse event isn’t always caused by the treatment tested in the trial.
- Antibody: A protein produced by the immune system that can attach to a pathogen such as the coronavirus and stop it from infecting cells.
- Approval, licensure and emergency use authorization: Drugs, vaccines and medical devices cannot be sold in the United States without gaining approval from the Food and Drug Administration, also known as licensure. After a company submits the results of clinical trials to the F.D.A. for consideration, the agency decides whether the product is safe and effective, a process that generally takes many months. If the country is facing an emergency — like a pandemic — a company may apply instead for an emergency use authorization, which can be granted considerably faster.
- Background rate: How often a health problem, known as an adverse event, arises in the general population. To determine if a vaccine or a drug is safe, researchers compare the rate of adverse events in a trial to the background rate.
- Efficacy: The benefit that a vaccine provides compared to a placebo, as measured in a clinical trial. To test a coronavirus vaccine, for instance, researchers compare how many people in the vaccinated and placebo groups get Covid-19. Effectiveness, by contrast, is the benefit that a vaccine or a drug provides out in the real world. A vaccine’s effectiveness may turn out to be lower or higher than its efficacy.
- Phase 1, 2, and 3 trials: Clinical trials typically take place in three stages. Phase 1 trials usually involve a few dozen people and are designed to observe whether a vaccine or drug is safe. Phase 2 trials, involving hundreds of people, allow researchers to try out different doses and gather more measurements about the vaccine’s effects on the immune system. Phase 3 trials, involving thousands or tens of thousands of volunteers, determine the safety and efficacy of the vaccine or drug by waiting to see how many people are protected from the disease it’s designed to fight.
- Placebo: A substance that has no therapeutic effect, often used in a clinical trial. To see if a vaccine can prevent Covid-19, for example, researchers may inject the vaccine into half of their volunteers, while the other half get a placebo of salt water. They can then compare how many people in each group get infected.
- Post-market surveillance: The monitoring that takes place after a vaccine or drug has been approved and is regularly prescribed by doctors. This surveillance typically confirms that the treatment is safe. On rare occasions, it detects side effects in certain groups of people that were missed during clinical trials.
- Preclinical research: Studies that take place before the start of a clinical trial, typically involving experiments where a treatment is tested on cells or in animals.
- Viral vector vaccines: A type of vaccine that uses a harmless virus to chauffeur immune-system-stimulating ingredients into the human body. Viral vectors are used in several experimental Covid-19 vaccines, including those developed by AstraZeneca and Johnson & Johnson. Both of these companies are using a common cold virus called an adenovirus as their vector. The adenovirus carries coronavirus genes.
- Trial protocol: A series of procedures to be carried out during a clinical trial.
The briefing materials also provide a deeper look at the safety of the vaccine. In any large clinical trial, some people who get vaccines experience health conditions that have nothing to do with the vaccine itself. Comparing their rates of symptoms with those of the placebo group as well as with background rates in a population can point to symptoms that may actually be caused by a vaccine.
The F.D.A. concluded that there were no “meaningful imbalances” in serious health complications, known as adverse events, between the two groups. The agency noted that four people in the vaccinated group experienced a form of facial paralysis called Bell’s palsy, with no cases in the placebo group. The difference between the two groups wasn’t meaningful, and the rate in the vaccinated group was not significantly higher than in the general population.
The new Pfizer analysis revealed that many volunteers who received the vaccine felt ill in the hours after the second dose, suggesting that many people might have to request a day off work or be prepared to rest until the symptoms subside. Among those between ages 16 and 55, more than half developed fatigue, and more than half also reported headaches. Just over one-third felt chills, and 37 percent felt muscle pain. About half of those over age 55 felt fatigued, one-third developed a headache and about one-quarter felt chills, while 29 percent experienced muscle pain.
“Taking a day off after the second dose is a good thing to anticipate,” Dr. Iwasaki said.
On Monday, Kristen Choi, a psychiatric nurse and health services researcher at the University of California, Los Angeles, published a first-person account of the symptoms she experienced as a participant in the Pfizer-BioNTech trial, which included chills, nausea, headache and fever.
“Clinicians will need to be prepared to discuss with patients why they should trust the vaccine and that its adverse effects could look a lot like Covid-19,” Dr. Choi wrote in the journal JAMA Internal Medicine. She advised doctors to tell patients that these unpleasant symptoms were “a sign that the vaccine is working, despite the unfortunate similarities with the disease’s symptoms.”