Moderna COVID-19 Vaccine

(mRNA-1273 SARS-CoV-2 vaccine)

Moderna COVID-19 Vaccine

(mRNA-1273 SARS-CoV-2 vaccine)
Browsing COVID-19 vaccine clinical trials

Moderna Vaccine Summary

All information in this page has been gathered from Moderna's phase 3 clinical trial, unless otherwise referenced.

Vaccine Effectiveness

  • 100% effective for prevention of severe COVID-19
  • 94.1% effective for prevention of symptomatic COVID-19

Vaccine Safety

  • Most common side effects
    • Injection site: Pain, redness, swelling
    • General: Fever, fatigue, muscle pain, chills, nausea
  • Likelihood of serious side effects were the same as placebo
    • Vaccine group: 0.6%
    • Placebo group: 0.6%
  • Individuals who are hypersensitive (seriously allergic) to vaccine ingredients (see below) should avoid the Moderna vaccine

Vaccine Administration

  • 2 intramuscular injections, separated by 4 or more weeks

General Moderna Vaccine Information


What are other names for this vaccine?

COVID-19 vaccines are commonly identified by the name of their manufacturer. In this case that is Moderna. The scientific name for this vaccine is the mRNA-1273 SARS-CoV-2 vaccine.

How does this vaccine work?

Moderna’s COVID-19 vaccine is a mRNA-based vaccine. In your body, the mRNA in the vaccine makes a spike protein, a harmless part of the coronavirus that causes COVID-19. This trains your immune system to recognize and attack the spike protein so that if you are exposed to the real coronavirus, your immune system will react much more quickly and effectively to prevent you from developing COVID-19 (especially severe COVID-19).

What are the ingredients?

Ingredient Purpose
Messenger RNA (mRNA) Active component of the vaccine
Fats Protect the mRNA
Salt/buffer Keeps the vaccine at proper pH and makes the vaccine injection more comfortable to receive
Sugar Protects the mRNA during freezing
Water Makes the vaccine an injectable fluid

The Moderna vaccine does NOT contain preservatives, aluminum, or mercury.

How many doses are required?

Moderna’s COVID-19 vaccine was studied as two intramuscular injections administered 4 weeks apart.

However, Canada’s National Advisory Committee on Immunization (NACI) (an expert advisory body to the Public Health Agency of Canada [PHAC]) has advised that second doses of COVID-19 vaccines can be administered up to 4 months after the first dose. This NACI recommendation is based on data that showed a single dose of the Moderna vaccine was still effective in preventing COVID-19, and to allow more people to receive their first dose during the current vaccine shortage (NACI summary).

What temperature does this vaccine need to be stored at?

  • Moderna’s COVID-19 vaccine should be stored in the freezer between -15°C to -25°C.
  • Vials can be stored refrigerated between 2°C to 8°C for up to 30 days prior to first use.
  • Unpunctured vials may be stored between 8°C to 25°C for up to 12 hours.

In what types of people has this vaccine been studied?

The Moderna vaccine was studied in adults 18 years of age or older who had not had COVID-19 before. This included both healthy adults and those with stable pre-existing medical conditions.

People who were sick, immunosuppressed, or had an unstable pre-existing medical condition were not included in the initial trial but more data are being gathered as countries around the world vaccinate people with these characteristics.

Are there any groups of people that this vaccine is NOT recommended for?

The Moderna vaccine should not be given to people who are allergic to the active ingredient or to any ingredients in the formulation (see above for the Moderna vaccine ingredient list).

Is the Moderna vaccine safe?


What are the side effects and the frequency that they occur?

The most common side effect of the Moderna vaccine is pain at the site of injection. Other less common side effects include fever, headache, fatigue, and muscle pain. Serious side effects can occur, but these are very rare and in the phase 3 clinical trial there was no difference between the rates of severe side effects in the placebo group compared to the group that received the vaccine. 

In general, side effects are more common and more severe after the second dose compared to the first dose.

Will this vaccine make me “sick”? 

No. The side effects that are experienced after receiving any vaccine, including Moderna’s COVID-19 vaccine, are caused by the body’s immune system  responding to the vaccine to prepare to protect the body from the virus.

How do I treat side effects of the vaccine?

To treat fever/pain, you can take Tylenol (acetaminophen). Rest, adequate diet and fluid intake will help as well.

What are the long-term effects of the vaccine?

Since this vaccine is so new, it’s impossible to be entirely sure what the long-term effects may be. What we do know is that millions of people have been vaccinated with mRNA vaccines and we have no indication that there are any long-term negative health impacts. People who have received the Moderna vaccine as part of the Phase 3 clinical trial are followed for 2 years after their second dose to continue to monitor for the health effects of the vaccine. In a similar way, governments around the world have reporting systems in place to identify negative health events following vaccines (i.e. the Canadian Adverse Events Following Immunization Surveillance System [CAEFISS]).

Despite how new these vaccines are, it is important to place the potential vaccine risks within the context of the current pandemic. The known negative health and population impacts of COVID-19 are much greater than the potential negative health impacts of the Moderna vaccine.

Is the Moderna vaccine effective for preventing COVID-19?

What does vaccine “efficacy” mean and how was it measured?

Efficacy in relation to COVID-19 vaccines is the measure of how effective the vaccine is in preventing COVID-19 infection compared to a placebo. Since this is hard to calculate in the real world, the efficacy numbers that we know are what is found in phase 3 clinical trials.

How effective is the Moderna vaccine? (What is the vaccine's efficacy?)

According to data from Moderna’s phase 3 clinical trial, the Moderna vaccine is 94.1% effective in preventing symptomatic COVID-19 infection. There were also no incidences of severe COVID-19 infection found in the people that received the Moderna vaccine and 30 cases of severe COVID-19 in the people that did not receive the vaccine. This indicates that Moderna’s vaccine likely protects against severe COVID-19 infection.

How long after injection before this vaccine starts working?

Once the Moderna vaccine is injected, your body takes time to react and develop an immune defense. The exact amount of time required for someone to be protected from developing COVID-19 is not known, however, the trial did show that there was some protection starting 14 days after the first dose. Full vaccine efficacy in the phase 3 clinical trial is measured 14 days after the second dose.

Will the vaccine prevent asymptomatic COVID-19?

The phase 3 clinical trial for Moderna’s vaccine focused on symptomatic COVID-19 cases and did not have sufficient data to make conclusions about the effectiveness of the Moderna vaccine in preventing asymptomatic infection.

Can I still transmit COVID-19 after being vaccinated?

There is not enough data available to answer this question.

Does the Moderna vaccine work against new COVID-19 variants of concern?

Moderna has completed one study on the effectiveness of the Moderna COVID-19 vaccine on the COVID-19 variants first discovered in the UK (B.1.1.7) and in South Africa (B.1.351). This showed that the Moderna vaccine was equally effective in neutralizing the B.1.1.7 variant compared to the original coronavirus strain, but had a reduced effectiveness against the B.1.531 variant.

The effectiveness of the Moderna vaccine on the COVID-19 variant first discovered in Brazil (P.1) is still unknown.

Population-specific recommendations

Health Canada and the United States Food and Drug Administration (FDA) have both approved the Moderna vaccine for use in all adults (age 18 years or older) who are not hypersensitive to any ingredients in the formulation. This includes all other special populations, but there are many individual-specific considerations that should go into the choice to receive this vaccine if you fall into one of the following groups. General information is listed below, but please consult a medical professional if you are uncertain if the Moderna vaccine is appropriate for you.