But fewer cases of Covid-19 occurred among trial participants in the early days of the Moderna trial, making it more difficult to measure the differences between the vaccinated group and the placebo group. Either way, health officials have said that for both vaccines, two doses are essential for full protection.
A second difference concerns the ability to prevent serious illness. Moderna has produced more evidence that its vaccine can do this, according to the journal. In his trial, 30 volunteers developed severe cases of Covid. All were in the placebo group, with no cases among those vaccinated.
In the Pfizer-BioNTech trial, the results were less convincing. There were 10 serious cases in the placebo group and one in the vaccinated group. These numbers are too small to assess the vaccine’s ability to prevent serious disease.
“The data available for these results did not allow any definitive conclusions to be drawn,” the FDA said.
Documents released on Tuesday made it clear that side effects were particularly common after the second dose, but usually only lasted a day. Experts say people may need to take time off work after being vaccinated.
During the Moderna trial, researchers also kept an eye out for volunteers who developed new disorders. In a multi-month trial with 30,000 volunteers, it’s normal for some to suffer from conditions unrelated to the vaccine, health experts say. Comparing the rates between people who receive the vaccine and the placebo – as well as general baseline rates – can help identify serious concerns and rule out coincidences.
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- ACE-2: A protein that is found on the surface of certain types of human cells. The coronavirus must bind to ACE-2 to enter cells.
- Adverse event: A health problem that arises in volunteers during a clinical trial of a vaccine or drug. An adverse event is not 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 coronavirus and prevent it from infecting cells.
- Antiviral drug: A drug that interferes with the ability of a virus to replicate inside cells. The first drug approved for Covid-19 in the United States, remdesivir, is an antiviral.
- Emergency use approval, license and authorization: Medicines, vaccines and medical devices cannot be sold in the United States without winning approbation of the Food and Drug Administration, also known as license to practice. After a company submits clinical trial results to the FDA for review, the agency decides whether the product is safe and effective, a process that typically takes several months. If the country is faced with an emergency – such as a pandemic – a company can request a emergency use authorization, which can be granted much faster.
- Compassionate Use: Term used to describe treatments given to seriously ill people although they have not yet been approved by the Food and Drug Administration for this use.
- Cytokine storm: An overactive immune system response that can lead to massive inflammation and tissue damage. Cytokine storms may be responsible for many severe cases of Covid-19, and a number of researchers are testing drugs that may be able to calm them down.
- Interferon: A molecule made by the immune system. Some types of interferons can trigger inflammation in the body, while others reduce it. However, other types can cause cells to strengthen their defenses against viruses. Researchers are studying whether synthetic interferon treatments can help people fight the coronavirus.
- Monoclonal antibodies: Monoclonal antibodies, created in the laboratory, mimic natural antibodies produced by the immune system. A number of companies have developed these treatments for Covid-19. President Trump received Regeneron’s antibody treatment shortly after being diagnosed with the disease.
- Phase 1, 2 and 3 trials: Clinical trials generally take place in three stages. Phase 1 trials typically 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 different doses and collect 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 while waiting to see how many people are protected from the disease they are supposed to be fighting for.
- Placebo: A substance with no therapeutic effect, often used in a clinical trial. To see if a vaccine can prevent Covid-19, for example, researchers can inject half of their volunteers with the vaccine, while the other half are given a saltwater placebo. They can then compare the number of people in each group infected.
- Post-market surveillance: The follow-up that takes place after the approval of a vaccine or drug and which is regularly prescribed by doctors. This usually confirms that the treatment is safe. On rare occasions, it detects side effects in certain groups of people that were missed in clinical trials.
- Preclinical research: Studies that take place before the start of a clinical trial, usually involving experiments where a treatment is tested in cells or in animals.
- Test protocol: A series of procedures to be performed during a clinical trial.
- Retrospective study: A study that analyzes data collected in the past to assess the effectiveness of a treatment. Retrospective studies can offer useful information, but are not as definitive as randomized clinical trials.
- Peak protein: A protein that is found 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 (RBD). Once the protein is attached, the virus can enter the cell. Many vaccines and monoclonal antibody treatments are designed to attach to the peak.
- Standard of care: A treatment accepted by medical experts as an appropriate way to treat a certain type of disease. Once a standard of care emerges for a disease, any new experimental treatment is usually tested against it, rather than a placebo.
During the Moderna trial, three vaccinated participants developed a form of temporary facial palsy called Bell’s palsy, while one participant on the placebo also experienced it. Bell’s palsy, which can last for weeks or more, can be triggered by viral infections and other causes. Some 40,000 people develop the disease each year in the United States. Years of intense research have failed to find evidence that any vaccine routinely recommended in the United States causes Bell’s palsy.
In the review published Tuesday, the FDA said, “There is insufficient information currently available to determine a causal relationship with the vaccine. “