Flu vaccine

It is highly recommended that people most at risk of developing complications get vaccinated each year in order to protect themselves. For these people, vaccination is the best protection against the flu and its complications.

Vaccination allows the body to make antibodies to fight the flu. However, studies have shown that the number of antibodies may decrease in the year after vaccination. This decrease particularly affects older adults and people with a weakened immune system.

In addition, viruses that cause flu constantly change. The composition of flu vaccines are reviewed annually in order to include the virus strains most likely to be in circulation during the flu season.

Consult the details of the Flu Vaccination Program to know how to proceed and where to get vaccinated.

For the 2022-2023 season, two forms of the flu vaccine are offered in Québec:

• injectable flu vaccine (only free vaccine offered by the Flu Vaccination Program);
• intranasal flu vaccine.

Flu vaccine is safe. It cannot transmit flu or other illnesses. In fact, it contains part of the viruses or viruses that are killed or too weak to reproduce and cause the flu.

In Canada and at the World Health Organization (WHO), there are several vaccination surveillance programs. These programs ensure, among other things, the quality of vaccines offered. Among these is the Québec surveillance program, ‘Effets secondaires possiblement reliés à l’immunisation’ (ESPRI). This program was established in 1990 by the Ministère de la Santé et des Services sociaux.

The flu vaccine does not make COVID-19 symptoms worse if you get infected.

The flu vaccine generally takes 2 weeks before being fully effective.

The protection offered by the vaccine may vary from person to person, but it lasts at least 6 months. 

The vaccine protects only against the strains of the flu virus it contains. It does not protect against other respiratory infections such as the cold or COVID-19. Flu is often confused with cold. To learn more, go to the Differences between flu and cold page.

Factors that determine effectiveness

The vaccine’s effectiveness depends on the following:

• The age of the person vaccinated
• The state of the person’s immune system, meaning the system that allows their body to defend itself against infections
• The degree of kinship between the virus strains circulating and those contained in the vaccine

The vaccine therefore does not offer 100% protection against the flu. The vaccine prevents the flu in about 40 to 60% of healthy people when the strains of viruses it contains correspond to strains circulating.

A strain of the virus included in the vaccine may not match the circulating strains. Indeed, the virus can evolve differently from what was predicted. As a result, the vaccine will be less effective against this strain. Nonetheless, the annual flu vaccine is still recommended, since it protects against the other strains included the vaccine that might be circulating.

For people aged 75 and over and those with chronic illnesses, the vaccine especially help reduce the risks of complications from the flu, hospitalisation and death.

Vaccination is recommended for children between the age of 6 months and 17 years who have certain chronic diseases to ensure they are effectively protected against the flu and its complications. To reduce the risk of complications, vaccination is also offered free of charge to members of the same household and informal caregivers of these children.

If vaccination is recommended for your child and he does not feel well enough on the day of vaccination, go to the Conditions for postponing vaccination section to find out whether or not you need to postpone his vaccination.

Here is some information on vaccinating children according to their age:

• Children less than 6 months old
• Children less than 9 years old
• Children aged 9 and up

It is not recommended to vaccinate children aged less than 6 months. Indeed, the effectiveness of the vaccine has yet to be proven for children that age. The vaccine is therefore not offered to them.

However, children under 6 months of age can also catch the flu. Furthermore, they are among those who are more at risk of being hospitalized after the flu. Therefore, vaccination is recommended for members of the same household and informal caregivers of children under 6 months of age to avoid passing on the flu to them.

If you are a member of the same household or the informal caregivers of a child under 6 months of age, you can get vaccinated free of charge under the Flu Vaccination Program.

Children less than 9 years old getting the flu vaccine for the first time must receive 2 doses of vaccine. The second dose must be given a month after the first. Parents must therefore plan 2 appointments to get their child a flu vaccination.

Indeed, as most vaccines given in childhood, the first injection of the flu vaccine must be followed by a second dose. The first dose of the vaccine allows the child’s immune system to, in a way, ‘get acquainted with the virus’ and to fight it, but for only a few weeks. The second dose allows the child’s immune system to produce more antibodies to fight the virus on a longer term.

It is therefore important that children less than 9 years old getting the flu vaccine for the first time receive the 2 doses of vaccine. The second dose will allow them to be best protected during the entire flu season.

Only children less than 9 years old who have already received the flu vaccine need to receive a single dose of it.

Children from 6 to 23 months old and those who have certain chronic diseases can get vaccinated free of charge under the Flu Vaccination Program.

From the age of 9, children that get the flu vaccine receive a single dose of it, even if they have never received a flu vaccine before.

The immune system of a 9 years old child is indeed sufficiently developed to produce enough antibodies to protect them with a single dose of the vaccine.

Children who have certain chronic diseases can get vaccinated free of charge under the Flu Vaccination Program.

If you have a fever or any other symptoms of COVID-19, or if you have received instructions from public health to self-isolate because of COVID-19, you must postpone getting vaccinated.

Some reactions may occur following vaccination:

• Symptoms of injectable vaccine
• Symptoms of intranasal vaccine