A flu shot is recommended to prevent a flu virus infection and to reduce the risk for flu complications, like pneumonia, respiratory failure, hospitalization and even death. It can be administered to younger and older adults, and children after 6 months of age.

This vaccine helps the body develop immunity against the main viruses that cause influenza, such as Influenza A (including subtypes H1N1 and H3N2), and Influenza B. The components in the vaccine are altered every year to protect against new mutations of the virus.

Be sure to speak to your family doctor or pharmacist regarding where and how you can get the flu shot this year.

When is it indicated

The flu shot is mainly indicated during flu season for people who are more likely to come into contact with the flu virus or develop serious symptoms and/or complications. This population of patients includes:

Children between 6 months and 6 years of age
Older adults over 60 years old
Pregnant or postpartum women up to 45 days after labor
Health care providers
Teachers
Indigenous population
People with compromised immune systems with a history of diseases like HIV or cancer, for example
People with chronic disease, such as diabetes, bronchitis or asthma
Patients with trisomy disorders, like Down syndrome
Navy, army and aeronautics professionals
Civil, military, road and federal police, municipal guards and firefighters

Furthermore, professionals who work within the prison system, prisoners, and teenagers living in institutions should also be vaccinated, as these types of facilities are associated with a higher transmission rate.

Most flu campaigns will kick off with vaccination first prioritized for more vulnerable populations, and then open access to other members of the community.

Flu shot types

There are two types of flu shots which are:

1. Trivalent flu vaccine

The trivalent flu vaccine is a split virion, inactivated vaccine that is effective against Influenza A viruses, subtypes H1N1 and H3N2, and Influenza B.

2. Tetravalent flu vaccine

The tetravalent flu vaccine is also a split virion, inactivated vaccine, but it protects against 2 subtypes of Influenza A (H1N1 and H3N2) and 2 strains of influenza B. The 2 strains of influenza it covers varies, depending on the mutation of the virus that circulated in the previous year.

When to take

The flu shot schedule is typically maintained as follows:

Adults: 1 dose, once a year;
Babies over 6 months and children up to 9 years old: 2 initial doses, the first dose being on the date chosen by the doctor and the second dose administered 30 days after the first dose. After the initial doses, 1 dose is recommended, once a year.

The location on the body for the flu shot may vary depending on age. In children under 18 months, the vaccine must be administered to the left thigh, while in children over 18 months and adults, the vaccine is administered in the non-dominant arm.

Possible side effects

The most common side effects of the flu shot are:

1. Headaches and muscle or joint aches

Some people may experience fatigue, body aches and headaches, which may appear about 6 to 12 hours after vaccination.

What to do: you should rest and drink plenty of fluids. If the pain is severe, you can take analgesics, such as acetaminophen as prescribed by a doctor.

2. Fever, chills and excessive sweating

Some people may also feel fever, chills and sweat more than normal after vaccination. These are usually temporary symptoms, which appear 6 to 12 hours after vaccination, and disappear within about 2 days.

What to do: If fevers, chills or sweating is intense, you can take analgesics like acetaminophen, as approved by your doctor.

3. Injection site reactions

Another common adverse reactions of the flu shot is pain, redness, a hard bump or swelling at the injection site.

What to do: You can apply a cold compress wrapped in a clean cloth to the area. However, a very extensive injury or limited movement of the arm should be assessed by a doctor immediately.

Contraindications for use

The flu shot is contraindicated for people with egg or latex allergies, as well as for people who have had a serious allergic reaction to a previous dose of the vaccine. In any case, if you have any questions about whether you are a good candidate for this vaccine, you should consult your doctor.

People presenting with an acute, moderate to severe fever should also not receive a flu shot. They are advised to wait for symptoms to subside.

Common questions

Some common questions regarding the flu shot are:

1. Does the vaccine protect against H3N2, H1N1 or COVID?

Most publically-funded vaccines protects against 3 types of the Influenza virus: influenza A (H1N2 and H3N2) and Influenza type B, which is why it is referred to as a trivalent vaccine.

However, this vaccine does not protect against any type of coronavirus, including the one that causes COVID-19 infection.

2. Do I need to have a flu shot every year?

The flu shot is effective for 6 to 12 months, which is why it should be administered every year, ideally in the fall.

Furthermore, because flu viruses mutate rapidly, the new vaccine ensures that you are protected against new types of the influenza virus that have emerged throughout the year.

Once administered, the flu shot begins to take effect within 2 to 4 weeks. Therefore, it is not capable of preventing a flu that is already developing.

3. When can I get my flu shot?

Ideally, the vaccine should be administered up to 4 weeks before any flu symptoms appear. However, if the person already has the flu, it is advisable to wait for the symptoms to disappear before getting vaccinated. This can help to differentiate whether symptoms are related to the flu virus or a vaccine reaction.

4. Can I get the flu and COVID vaccine together?

The CDC confirms that the flu and COVID-19 vaccines can be administered during the same visit, as long as they are applied to different muscle groups. Getting them on the same day will not interfere with the effectiveness of the vaccines.

5. Can pregnant women get a flu shot?

During pregnancy, a woman's body is more vulnerable to infections. Therefore pregnant women are at a higher risk for catching the flu, and should get their flu shot.