The Moderna vaccine is one of the vaccines currently available in the United States and other countries to protect against COVID-19, which is the disease the novel coronavirus causes.

Clinical trials and real world data suggest that the Moderna vaccine effectively and safely protects adults against the virus and its complications.

This article will discuss the efficacy of the Moderna COVID-19 vaccine as well as its potential side effects. It will also consider the benefits of getting a COVID-19 vaccine, including its potential role in ending the pandemic.

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The Moderna vaccine is also known as the mRNA-1273 vaccine. It is one of the vaccines currently available to protect people against COVID-19.

Moderna are an American pharmaceutical and biotechnology company who research and develop drugs and vaccines.

The Food and Drug Administration (FDA) issued emergency use authorization (EUA) for the vaccine in December 2020. Since then, Canada, the European Union, and the United Kingdom have also authorized its use.

The Moderna COVID-19 vaccine contains the following:

  • messenger ribonucleic acid (mRNA)
  • lipids SM-102, polyethylene glycol (PEG) 2000 dimyristoyl glycerol, and 1,2-distearoyl-sn-glycero-3-phosphocholine
  • cholesterol
  • tromethamine
  • tromethamine hydrochloride
  • acetic acid
  • sodium acetate
  • sucrose

Allergen information

It is free from:

The Moderna vaccine is an mRNA vaccine. These are new types of vaccines that work differently from other vaccines.

mRNA vaccines deliver the genetic code to our cells to make a protein that triggers the body’s immune response.

The body then produces antibodies and develops longer lasting immunity that can fight off the SARS-CoV-2 virus should it enter the body at a later stage.

Learn more about the body’s immune response to COVID-19 here.

Healthcare professionals will administer the vaccine in two separate doses.

They will give the vaccine as an injection into the upper arm, and they will administer the second dose 28 days after the first.

Vaccine logistics refers to how healthcare staff store the vaccine and how organizations distribute it to the wider population.


The FDA state that staff must store the Moderna COVID-19 vaccine frozen, between -13°F (-25ºC) and 5°F (-15ºC).

Staff can store the vaccine in the refrigerator between 36°F (2°C) and 46°F (8°C) for up to 30 days before use.

Once staff withdraw the first dose from a multidose vial, they should keep the vial at between 36°F (2°C) to 77°F (25°C). They should discard the vial after 6 hours because this vaccine does not contain any preservatives.


In the U.S., the Centers for Disease Control and Prevention (CDC) are managing the distribution of Moderna vaccines through the pharmaceutical distribution company McKesson.

McKesson also manage the Vaccines for Children Program, and they managed the distribution of the H1N1 vaccine during the swine flu pandemic.

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For more advice on COVID-19 prevention and treatment, visit our coronavirus hub.

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The Moderna vaccine is authorized for use in people aged 18 years and over. Governments will roll it out to the wider population according to vaccine availability and individual needs.

The CDC have given recommendations for who should receive the COVID-19 vaccine first. They recommend the following order for vaccinations:

  • Phase 1a: The first distribution phase will include the following people:
    • healthcare personnel
    • residents of long-term care facilities
  • Phase 1b: The second distribution phase will include the following people:
    • essential workers
    • people aged 75 years and older
  • Phase 1c: The third distribution phase will include the following people:
    • people aged 65–74 years
    • people aged 16–64 years with underlying medical conditions that increase the risk of serious complications from COVID-19
    • other essential workers

As the availability of COVID-19 vaccines increases, these vaccination recommendations will expand to include more groups.

However, it is important to note that these are CDC recommendations. Each U.S. state and each country will have its own plan for prioritizing the administration of the COVID-19 vaccines.

Before vaccination, individuals should tell their vaccine provider about their medical conditions. They should also inform them if they have any of the following:

A person should also inform their vaccine provider if they are any of the following:

  • immunocompromised
  • pregnant or planning to become pregnant
  • breastfeeding

A person should also tell the vaccine provider if they have previously received another COVID-19 vaccine.

Who should not get the vaccine?

The CDC advise that people with certain allergies should not get the Moderna vaccine. This includes people who have had allergic reactions to PEG or polysorbate and those who have had a severe allergic reaction, or an immediate allergic reaction of any severity, to any ingredient in an mRNA COVID-19 vaccine.

An immediate allergic reaction involves experiencing a reaction up to 4 hours after receiving the vaccine. Symptoms may involve:

mRNA vaccines such as the Moderna vaccine are unlikely to pose specific risks to pregnant people.

However, COVID-19 itself puts pregnant people at increased risk of severe illness, hospital admission, and death compared with non-pregnant people of a similar age.

COVID-19 may also cause adverse pregnancy outcomes, such as preterm birth.

The FDA do advise pregnant or breastfeeding people, as well as those who plan to become pregnant, to speak with their doctor about getting the vaccine.

Learn more about COVID-19 during pregnancy here.

When considering the effects of the Moderna vaccine on COVID-19, it is important to distinguish between effectiveness and efficacy.

Efficacy refers to how something performs under ideal and controlled circumstances, such as in clinical trials.

Effectiveness, on the other hand, describes the performance of something in “real world” situations.

Learn more about vaccine efficacy vs. effectiveness here.


A large 2020 trial, involving 30,420 adult volunteers at various sites across the U.S., reports that the Moderna vaccine has a 94.1% efficacy rate against COVID-19, including against severe disease.

The average age of participants was 51.4 years, with 24.8% aged 65 years or older. Just over half of the participants (52.7%) were male. The majority of participants were white (79.2%), with racial and ethnic demographics generally representative of U.S. demographics (10.2% Black or African American and 20.5% Hispanic or Latino).


Another study, which has yet to undergo peer review, investigated the real world effectiveness of the Moderna and Pfizer vaccines. The researchers compared 31,069 vaccinated individuals (having received at least one dose of either vaccine) with 31,069 unvaccinated people.

The findings suggest that getting both doses of either COVID-19 vaccine was 88.7% effective in preventing infection.

Those who did get COVID-19 following vaccination had significantly lower 14-day hospital admission rates than unvaccinated people of a similar demographic.

According to the World Health Organization (WHO), the evidence so far indicates that the Moderna vaccine is effective against the new variants of COVID-19.

These new variants include those that scientists first identified in the U.K. and South Africa.

Preliminary data suggest that the Moderna vaccine may offer some level of protection against transmission to others. It may even prevent symptomatic infection after just the first dose.

However, research into this is still ongoing, and no definitive conclusions are possible just yet.

The most common side effects of the Moderna COVID-19 vaccine are:

These symptoms may develop within a day or two of receiving the vaccine and may last for a few days.

Side effects are more likely after the second dose.

Methods to relieve these side effects may include:

Serious side effects, such as anaphylaxis, following vaccination with the Moderna vaccine are rare. Anaphylaxis is a life threatening allergic reaction that develops within minutes to hours of vaccination. It may cause the following symptoms:

Learn more about anaphylaxis here.

Other rare side effects following vaccination can include myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the tissue surrounding the heart). These side effects are more likely following the second dose of the vaccine.

Individuals who experience a severe allergic reaction should call 911 or go to the nearest emergency department.

Those who develop other side effects should speak with a pharmacist or doctor if these effects are persistent or bothersome.

The main benefit of getting a COVID-19 vaccine is protection against the symptoms and complications of COVID-19.

Vaccination may reduce the chance of transmitting the virus.

At present, it is unclear how long COVID-19 vaccine protection will last. As time goes on, this will become clearer. Until then, it is important that people who are vaccinated still wear a face mask, practice physical distancing, and regularly wash their hands.

Together with these measures, COVID-19 vaccines are important tools in stopping the pandemic. Once the pandemic is over, people can likely return to their previous activities, including spending time with friends and family.

Currently, the U.S. has authorized three vaccines for the prevention of COVID-19: the Moderna vaccine, the Pfizer-BioNTech vaccine, and the Janssen vaccine.

The Moderna vaccine has a similar efficacy to the Pfizer-BioNTech vaccine, which has an efficacy rate of 95%.

However, one benefit of the Moderna vaccine is that it is easier to store because it does not require temperatures as cold as the Pfizer vaccine.

Large-scale clinical trials for other vaccines, such as the AstraZeneca and Novavax vaccines, are also in progress or in the planning stages.

The AstraZeneca COVID-19 vaccine candidate currently demonstrates an efficacy of 63.09% against symptomatic COVID-19.

The Novavax COVID-19 vaccine​ candidate shows 89.3% efficacy in clinical trials, as well as 60–86% efficacy against emerging variants.

The phase 3 clinical trial of the Moderna vaccine did not identify any safety concerns, and there was no evidence of vaccine-associated enhanced respiratory disease (VAERD).

Scientists have observed cases of VAERD in situations where some people have received a particular vaccine and then come into contact with the pathogen later and developed severe disease. Examples of VAERD can include conditions such as measles or respiratory syncytial virus.

The FDA analyzed data from tens of thousands of study participants. The data suggest that the benefits from the vaccine outweigh any possible risks.

One of the risks of the vaccine is the potential for a severe allergic reaction. This, however, is a rare event.

Those who have allergies to any ingredients in the Moderna vaccine should not get this vaccine. They should discuss their options with a doctor.

Studies into the longer-term safety of the vaccine are ongoing.

Not everyone will receive a COVID-19 vaccine. Some people may be unable to get one due to health issues. Others may choose not to for various reasons.

The FDA state that it is an individual’s choice as to whether or not they receive the vaccine and that those who choose not to will not experience any changes in their standard medical care.

However, those who do not receive a vaccination will be at greater risk of developing COVID-19 and experiencing its complications. Therefore, they should take care to follow the guidelines of wearing a face mask, practicing physical distancing, and regularly washing their hands.

There may be other implications for those who do not get a vaccine, including in relation to inter-country travel.

Clinical trials and real world data suggest that the Moderna COVID-19 vaccine provides significant protection from the disease.

The Moderna vaccine appears to be safe for most people, though minor side effects are common. Serious reactions, however, are rare.

COVID-19 vaccines such as the Moderna vaccine are important tools in ending the pandemic.

However, until the pandemic ends, people should continue to wear face masks, practice hand hygiene, and physically distance themselves from others, even after they receive their vaccination.

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