How mRNA vaccines work
MRNA vaccines, like Pfizer-BioNTech and Moderna vaccines, tell your body's cells to make "spike proteins." The spike proteins are specific to the virus that causes COVID-19. Your immune system will respond to the spike proteins by making antibodies that will fight off infection. Your new antibodies will break down the spike proteins and get rid of them. Your new antibodies will protect you from symptomatic illness if you are exposed to the COVID-19 virus. It is not known if the vaccine can prevent infection and transmission. The vaccine does not contain the virus and so it cannot give you COVID-19.
The Pfizer-BioNTech and Moderna vaccines have been tested in large clinical trials to ensure they have met safety standards, and has been licensed and approved by Health Canada.
How viral vector-based vaccines work
Viral vector-based vaccines, like the AstraZeneca vaccine, use a harmless virus, such as an adenovirus, as a delivery system. This "vector" virus is not the virus that causes COVID-19. Adenoviruses are among the viruses that can cause the common cold. There are many different types of adenoviruses, and many have been used as delivery systems for other vector-based vaccines for decades.
When a person is given the vaccine, the vector virus contained within the vaccine produces the SARS-CoV-2 spike protein. This protein is found on the surface of the virus that causes COVID-19. This protein will not make you sick. It does its job and goes away.
Through this process, the body is able to build a strong immune response against the spike protein without exposing you to the virus that causes COVID-19.
Vaccine Benefits
Two doses of the Pfizer vaccine is 95 per cent effective against getting COVID-19 symptoms, and two doses of the Moderna vaccine is 94 per cent effective against getting COVID-19 symptoms.
After completing the two-doses of the approved mRNA vaccines, it may take another one to two weeks to achieve maximum protection against COVID-19. At this time, there is no information on the long-term protection with this vaccine.
The AstraZeneca COVID-19 vaccine showed an effectiveness of about 62 per cent in preventing symptomatic COVID-19 disease beginning two weeks after the second dose. This effectiveness rate is based on an analysis of results from participants who had received the two dose regimen that will be used in Canada.
There is a small chance that you may still get COVID-19 after being vaccinated. It is important to continue with public health measures such as physical distancing, wearing a mask, and staying home if you are sick. Health care and other staff must still wear personal protective equipment (PPE) even after they have been vaccinated.
Side Effects and Risks
Some people may experience side effects from the vaccine, but they will likely be moderate and resolve after a few days. Some of the symptoms are part of the body's response to developing immunity.
AEFI:
|
Vaccine | Placebo control |
---|
Dose 1
| Dose 2 | Dose 1
| Dose 2
|
---|
Pain at injection site
| Very Common
| Very Common |
Very Common | Very Common |
---|
Tenderness | NS | NS | NS | NS |
---|
Redness | Common | Common | Common | Rare |
---|
Swelling | Common | Common | Rare | Rare |
---|
Lymphadenopathy / Axillary swelling and tenderness
| NS | NS | NS | NS |
---|
Warmth | NS | NS | NS | NS |
---|
Pruritis | NS | NS | NS | NS |
---|
Induration | NS | NS | NS | NS |
---|
AEFI:
|
Vaccine | Placebo control |
---|
Dose 1
| Dose 2 | Dose 1
| Dose 2
|
---|
Pain at injection site
| Very Common
| Very Common |
Very Common | Very Common |
---|
Tenderness | NS | NS | NS | NS |
---|
Redness | Common | Common | Uncommon | Uncommon |
---|
Swelling | Common | Very Common
| Uncommon | Uncommon |
---|
Lymphadenopathy / Axillary swelling and tenderness
| Very Common
| Very Common
| Common | Common |
---|
Warmth | NS | NS | NS | NS |
---|
Pruritis | NS | NS | NS | NS |
---|
Induration | NS | NS | NS | NS |
---|
AEFI:
|
Vaccine | Placebo control |
---|
Dose 1
| Dose 2 | Dose 1
| Dose 2
|
---|
Pain at injection site
| Very Common
| Very Common |
Very Common | Very Common |
---|
Tenderness | Very Common | Very Common | Very Common | Very Common |
---|
Redness | Common | Common | Common | Uncommon |
---|
Swelling | Common | Common | Common | Common |
---|
Lymphadenopathy / Axillary swelling and tenderness
| NS | NS | NS | NS |
---|
Warmth | Very Common | Very Common | Very Common | Very Common |
---|
Pruritis | Common
| Common | Common | Common |
---|
Induration | Common
| Uncommon | Common | Common |
---|
AEFI: adverse event following immunization
NS: not solicited
In rare cases, serious allergic reactions (anaphylaxis) can occur. Allergic reactions can be treated and are usually temporary. Seek medical attention if you have trouble breathing, have hives or swelling of the face and throat. Vaccine side effects will continue to be monitored as people receive the vaccine. If you get a reaction to the vaccine, contact your health care provider who will report the side effect directly to public health. Public health will keep track of the reported side effects to make sure the vaccine continues to be safe.
Precautions
- Delay getting vaccinated if you have a fever or are sick with COVID-19 symptoms.
- Pregnant and breastfeeding women can get the vaccine, as long as they have talked to their healthcare provider.
Do not get this vaccine, if you:
- are under 16 years of age for the Pfizer-BioNTech vaccine, under 18 years of age for the Moderna and AstraZeneca vaccines;
- have an autoimmune disorder or a weakened immune system due to illness or treatment (unless you have consulted with your healthcare provider about the risk versus benefits); or
- have an allergy to an ingredient in the vaccine or had a previous severe reaction to this vaccine (consult your health care provider).