The Moderna COVID-19 vaccine is a two-dose vaccine to prevent COVID-19. This Snapshot feature looks at the possible side effects and safety recommendations associated with this mRNA vaccine.
All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub for the most recent information on COVID-19.
Moderna’s COVID-19 vaccine, also known as mRNA-1273, is a two-dose vaccine. The doses are administered 28 days apart, and the vaccine trains the immune system to fight against future infections with SARS-CoV-2, the virus that causes COVID-19.
Moderna’s vaccine has authorization for use in a total of 53 countries. The
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Clinical trial data show that the vaccine has an efficacy of 94.1% at preventing symptomatic COVID-19.
Like the Pfizer-BioNTech vaccine, the Moderna vaccine is an mRNA vaccine. While these two are the first mRNA vaccines to be authorized for use in humans, scientists have been researching this technology for many years.
An mRNA vaccine functions by providing the body with genetic information to produce viral or bacterial proteins, in this case, the spike protein found on the surface of SARS-CoV-2. These proteins trigger an immune response and the production of specific antibodies, preparing the body to fight off an infection if it comes into contact with the pathogen in the future.
The vaccine only carries the information needed to make a small part of the virus. It does not contain the SARS-CoV-2 virus, and it cannot cause COVID-19.
Enzymes in our cells quickly degrade the mRNA molecules in the vaccine once the spike protein has been made. It is not possible for the vaccine to alter the body’s genetic information.
- fatigue (70%)
- headache (64.7%)
- muscle pain (61.5%)
- joint pain (46.4%)
- chills (45.4%)
- nausea and vomiting (23%)
- fever (15.5%)
The clinical trials found that side effects were more commonly reported after the second dose and lasted around 2–3 days.
Recipients also reported the following injection site reactions:
- pain (92%)
- swelling (14.7%)
- swelling of armpit lymph nodes, specifically (19.8%)
- redness (10%)
People who have had other authorized COVID-19 vaccines have also reported these side effects.
Among recipients of mRNA vaccines, however, there have been more frequent reports of side effects from people who have had the Moderna vaccine. This
There have also been reports of people experiencing a red, itchy, swollen, or painful rash at the injection site. Known as “
In the patient fact sheet for the Moderna vaccine, the FDA notes that symptoms of myocarditis or pericarditis tend to appear “within a few days following receipt of the second dose.” However, the FDA, adds, these side effects are very unlikely to occur in most people.
The federal agency also advises that those who do experience myocarditis or pericarditis symptoms after vaccination should seek medical attention immediately. The symptoms include chest pain, shortness of breath, and “feelings of having a fast-beating, fluttering, or pounding heart.”
According to the
Allergic reactions, severe and otherwise, have been reported as possible side effects of the vaccine, as a response to certain ingredients in the vaccine.
Anaphylaxis, a severe allergic reaction, is a rare side effect of vaccination. Out of
- difficulty breathing
- swelling of the face and throat
- a rapid heartbeat
- a rash all over the body
Like the Pfizer vaccine, the Moderna COVID-19 vaccine contains an ingredient called polyethylene glycol (PEG), which has
PEG, which is commonly found in laxatives, works in the vaccine as a protective coating for the mRNA molecule as it enters cells. It is still unclear whether PEG is the cause of the reported allergic reactions or whether the concentration of PEG in the vaccine is enough to cause a reaction.
It is worth noting that a PEG allergy is extremely rare. According to the
A possible explanation for this side effect is that the spike protein of the SARS-CoV-2 virus, which the mRNA helps the body to produce, interacts with regions around the dermal filler and induces an inflammatory response.
The agency says that people who have dermal fillers can have mRNA COVID-19 vaccines but that they should contact a healthcare professional if they experience any swelling after the vaccination.