Pfizer’s Vaccine Affords Robust Safety After First Dose

WASHINGTON – The coronavirus vaccine, manufactured by Pfizer and BioNTech, offers strong protection against Covid-19 within about 10 days of the first dose. This emerges from documents released Tuesday by the Food and Drug Administration ahead of a meeting of their vaccine advisory group.

The result is one of several significant new results in the newsletters, which includes more than 100 pages of data analysis from the Agency and Pfizer. Last month Pfizer and BioNTech announced that their two-dose vaccine had a 95 percent effectiveness rate after two doses three weeks apart. The new analyzes show that protection starts much earlier.

In addition, the vaccine worked well regardless of the race, weight, or age of a volunteer. While no serious adverse events from the vaccine were identified in the study, many participants experienced pain, fever, and other side effects.

“This is what an A + certificate looks like for a vaccine,” said Akiko Iwasaki, an immunologist at Yale University.

On Thursday, the FDA’s Vaccine Advisory Panel will discuss these materials prior to a vote on whether to recommend approval of the vaccine by Pfizer and BioNTech.

Pfizer and BioNTech started a large-scale clinical trial in July that recruited 44,000 people in the US, Brazil and Argentina. Half of the volunteers received the vaccine and half the placebo.

New coronavirus cases in the vaccinated group of volunteers quickly subsided about 10 days after the first dose, according to a graphic in the educational materials. The number of cases increased steadily in the placebo group.

The vaccine’s swift action could benefit not only the people who receive it, but also the strained hospitals in the country, limiting the flow of new patients to intensive care units.

Despite the early protection provided by the first dose, it is unclear how long this protection would last on its own, which underscores the importance of the second dose. Previous studies have shown that the second dose of the Pfizer BioNTech vaccine gives the immune system a significant long-term boost that is seen with many other vaccines.

The effectiveness of the vaccine after the first dose, according to Dr. William C. Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development, at about 52 percent. After the second dose, this value increases to about 95 percent. “Two doses of the vaccine offer maximum protection,” he said.

Many experts have raised concerns that the coronavirus vaccines might protect some people better than others. However, the results in the educational materials indicate no such problem. The vaccine has a high rate of effectiveness in both men and women, and similar rates in whites, blacks, and Latinos. It also worked well on obese people who are at higher risk of developing Covid-19.

Some vaccines for other diseases produce a weak immune response in older adults. However, Pfizer and BioNTech found that people over 65 received about as much protection from the coronavirus vaccine as younger people.

Even if the vaccine is approved by the FDA, the study will continue. In the briefing documents, the companies said they would encourage people to stay in the study for as long as possible without knowing whether they received the vaccine or the placebo, so the researchers can continue to gather information on whether the vaccine is safe and effective.

The road to a coronavirus vaccine

Interesting facts about vaccines

Confused by all of the technical terms used to describe how vaccines work and study? Let us help:

    • Adverse event: A health problem that occurs in volunteers in a clinical trial with a vaccine or drug. An adverse event is not always caused by the treatment tested in the study.
    • Antibody: A protein produced by the immune system that can attach to a pathogen such as the coronavirus and prevent it from infecting cells.
    • Approval, Licensing, and Approval for Emergency Use: Medicines, vaccines and medical devices cannot be sold in the US for no profit approval by the Food and Drug Administration, also known as Licensing. After a company submits the results of clinical studies to the FDA for review, the agency decides whether the product is safe and effective. This process usually takes many months. If the country faces an emergency – like a pandemic – a company can file an application instead Emergency approvalthat can be granted much faster.
    • Background rate: How often does the general population experience a health problem called an Adverse Event? To determine whether a vaccine or drug is safe, researchers compare the rate of adverse events in one study to the background rate.
    • Effectiveness: The benefit of a vaccine compared to a placebo, measured in a clinical trial. For example, to test a coronavirus vaccine, the researchers compare how many people in the vaccinated group and the placebo group are receiving Covid-19. In contrast, effectiveness is the benefit that a vaccine or drug offers in the real world. A vaccine’s effectiveness can be found to be less or more effective than its effectiveness.
    • Phases 1, 2 and 3 studies: Clinical trials typically take place in three phases. Phase 1 studies typically involve a few dozen people to determine whether a vaccine or drug is safe. In Phase 2 trials that involve hundreds of people, researchers can try different doses and take more measurements of the vaccine’s effects on the immune system. Phase 3 trials, involving thousands or tens of thousands of volunteers, determine the safety and effectiveness of the vaccine or medicine by waiting to see how many people are protected from the disease it is intended to be used against.
    • Placebo: A substance with no therapeutic effect that is widely used in clinical trials. For example, to see if a vaccine can prevent Covid-19, researchers can inject the vaccine into half of their volunteers while the other half are given a placebo with salt water. You can then compare how many people are infected in each group.
    • Post-market surveillance: The surveillance that occurs after a vaccine or drug has been approved and regularly prescribed by doctors. This monitoring usually confirms that the treatment is safe. Rarely, side effects are noted in certain groups of people that were overlooked during clinical trials.
    • Preclinical Research: Studies that take place prior to the start of a clinical trial typically include experiments that test a treatment on cells or animals.
    • Viral vector vaccines: A type of vaccine that uses a harmless virus to deliver immune-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 companies use a cold virus called adenovirus as a vector. The adenovirus carries coronavirus genes.
    • Test protocol: A series of procedures that must be performed during a clinical trial.

The educational materials also provide a deeper look into the safety of the vaccine. In any large clinical trial, some people who receive vaccines have health conditions unrelated to the vaccine itself. Comparing their symptom rates with those of the placebo group, as well as background rates in a population, may indicate symptoms that a vaccine may actually cause.

The FDA concluded that there were no “significant imbalances” between the two groups in serious health complications known as adverse events. The agency found that four people in the vaccinated group had a form of facial paralysis called Bell’s palsy, with no cases in the placebo group. The difference between the two groups was not significant and the rate in the vaccinated group was not significantly higher than in the general population.

The new Pfizer analysis found that many volunteers who received the vaccine felt sick in the hours after the second dose, suggesting that many people may need to request a day off or be willing to rest until symptoms appear ease up. Among the 16 to 55 year olds, more than half developed fatigue and more than half also reported headaches. Slightly more than a third experienced chills and 37 percent had muscle pain. About half of those over 55 felt tired, a third had a headache, and about a quarter felt chills, while 29 percent had muscle pain.

“Taking a day off after the second dose is a good thing to anticipate,” said Dr. Iwasaki.

On Monday, Kristen Choi, a psychiatric nurse and health care researcher at the University of California at Los Angeles, released a firsthand report on the symptoms she experienced as a participant in the Pfizer BioNTech study, including chills, nausea and headaches and fever.

“Doctors need to be prepared to discuss with patients why they should trust the vaccine and that its adverse effects could be very similar to Covid-19,” wrote Dr. Choi in JAMA Internal Medicine. She advised doctors to tell patients that these uncomfortable symptoms “are a sign that the vaccine is working despite the unfortunate similarities with the symptoms of the disease”.

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