However, in the early days of the Moderna study, there were fewer cases of Covid-19 among study participants, making it more difficult to measure the differences between the vaccinated group and the placebo group. In any case, health officials have said that for both vaccines, two doses are essential for complete protection.
A second difference concerns the ability to prevent serious illness. Moderna presented more evidence that its vaccine can, according to the review. In his study, 30 volunteers developed severe cases of Covid. All of them belonged to the placebo group, with no cases among the vaccinated people.
In the Pfizer BioNTech study, the results were less convincing. There were 10 severe cases in the placebo group and one in the vaccinated group. These numbers are too few to assess the vaccine's ability to prevent serious diseases.
"The data available for these results did not allow firm conclusions," according to the F.D.A. said.
The documents released on Tuesday made it clear that side effects were particularly common after the second dose, but usually lasted only one day. Experts say people may need to take a day off after the shot.
During the Moderna trial, researchers also kept an eye out for volunteers who developed new disorders. In a multi-month study of 30,000 volunteers, it's normal for some to suffer from conditions unrelated to the vaccine, health experts say. Comparing the rates between people receiving the vaccine and placebo, as well as general background rates, can help identify serious concerns and rule out coincidences.
New treatments for Covid-19
Things to know about Covid-19 treatment
Confused By The Terms To Treat Covid-19? Let us help:
- ACE-2: A protein that sits on the surface of certain types of human cells. The coronavirus has to bind to ACE-2 in order to penetrate cells.
- 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.
- Antiviral drug: A drug that affects the ability of a virus to replicate in cells. The first drug approved in the US for Covid-19, Remdesivir, is antiviral.
- 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 has submitted the results of clinical studies to the F.D.A. For testing purposes, 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.
- Compassionate Use: A term used to describe treatments given to seriously ill people even though they have not yet been approved for that use by the Food and Drug Administration.
- Cytokine storm: An overactive immune system reaction that can lead to massive inflammation and tissue damage. Cytokine storms can be responsible for many of the severe cases of Covid-19, and a number of researchers are testing drugs that may calm them down.
- Interferon: A molecule of the immune system. Certain types of interferons can cause inflammation in the body while others can contain it. Still other species can stimulate cells to strengthen their defenses against viruses. Researchers are investigating whether treating synthetic interferons can help people fight off the coronavirus.
- Monoclonal Antibodies: Monoclonal antibodies made in a laboratory mimic the natural antibodies made by the immune system. A number of companies have developed these treatments for Covid-19. President Trump received Regeneron's antibody treatment soon after the disease was diagnosed.
- Phases 1, 2 and 3 studies: Clinical trials typically take place in three stages. Phase 1 studies typically involve a few dozen people to determine whether a vaccine or drug is safe. In Phase 2 trials involving 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 drug by waiting to see how many people are protected from the disease it is supposed to be fighting.
- 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 typically confirms that the treatment is safe. In rare cases, 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.
- Test protocol: A series of procedures that must be performed during a clinical trial.
- Retrospective study: A study that analyzes data collected in the past to determine how effective a treatment is. Retrospective studies can provide useful information, but they are not as definitive as randomized clinical studies.
- Spike protein: A protein that sits on the surface of coronaviruses. The spike protein binds to the ACE-2 receptor on human cells using a region called the receptor binding domain (R.B.D.). As soon as the protein accumulates, the virus can enter the cell. Many vaccines and monoclonal antibody treatments are designed to stick to the tip.
- Standard of care: A treatment that is accepted by medical experts as an appropriate method to treat a specific type of disease. Once a standard for treating a disease is established, new experimental treatments are usually tested against it rather than a placebo.
During the Moderna study, three vaccinated participants developed a form of temporary facial paralysis called Bell's palsy, while one participant on the placebo experienced the same. Bell's palsy, which can last weeks or more, can be triggered by viral infections and other causes. Around 40,000 people develop this disease in the United States each year. Years of intense research have found no evidence that a vaccine routinely recommended in the US causes Bell's palsy.
In the review published on Tuesday, the F.D.A. said: "There is insufficient information currently available to establish a causal link with the vaccine."