Comprehensive Guide to the Seasonal Flu Vaccine

medica-seed-editor · November 4, 2026, 2:15pm

The seasonal flu vaccine helps reduce the severity of symptoms and limits the likelihood of hospitalization, serving as an effective way to protect those most prone to complications.

What is the seasonal flu vaccine and how does it work?

This vaccination relies on using inactivated or attenuated versions of the virus, meaning it cannot cause the disease. Scientists identify 3 or 4 strains of the virus expected to spread before the season begins, and the vaccine is manufactured based on these findings.

Available vaccine types vary:

Trivalent vaccine: Provides protection against two type (A) strains and one type (B) strain.
Quadrivalent vaccine: Adds a second type (B) strain to increase the range of protection.

Vaccine types and administration methods

There are several ways to receive a flu vaccination depending on the type of vaccine and the patient’s health status:

Inactivated vaccine: Administered via intramuscular injection; suitable for those aged 6 months and older.
Attenuated vaccine: Available as a nasal spray for people aged 2 to 49 years; not recommended for pregnant women.
Recombinant vaccine: Specifically for individuals aged 18 years and older.

Groups most in need of vaccination

Certain groups are more susceptible to health risks, making vaccination essential, including:

Older adults (65 years and older).
Pregnant women, children, and infants over 6 months.
Individuals with chronic diseases such as diabetes, heart, kidney, or liver diseases, and chronic lung diseases.
People with immunodeficiency or neurological conditions such as multiple sclerosis.
Healthcare workers.

Contraindications and warnings

There are cases where the vaccine should be avoided or postponed:

Children under 6 months of age.
Those with severe allergies to vaccine components (such as gelatin or antibiotics).
Individuals with a history of Guillain-Barré syndrome who are not at high risk of contracting the flu.
Vaccination should be postponed if a fever is present, though it can be administered during a respiratory illness without fever.
Regarding egg allergies, those with mild allergies can receive the vaccine, while severe allergies require close medical supervision.

Side effects and post-vaccination tips

Some mild influenza symptoms may appear as side effects, such as pain and swelling at the injection site, headache, or general fatigue. The nasal spray may cause a runny nose or sore throat.

The body takes a period ranging from two weeks (or 5 to 10 days according to some sources) to build immunity. During this time, it is recommended to:

Wash and sanitize hands constantly.
Avoid touching the face, nose, and mouth.
Stay away from crowded places.

Frequently Asked Questions

What are the side effects of the quadrivalent vaccine?

These range from pain at the injection site, mild fever, and muscle aches. If the nasal spray is used, a runny nose, cough, or headache may occur.

Is it recommended to get the vaccine annually?

Yes, it is recommended every year because the strains are updated annually to ensure effectiveness against the viruses expected to spread each season. This is particularly important for managing seasonal flu in children.

Does the vaccine protect against stomach flu?

No, the vaccine is designed only for viruses that affect the respiratory system and does not protect against gastroenteritis caused by other viruses such as “Norovirus” and “Rotavirus.”

When to visit a doctor?

Consult a doctor immediately if severe allergic signs appear after vaccination, such as:

Difficulty breathing.
Angioedema (swelling) or severe dizziness.
Persistent vomiting.

Medical Disclaimer: This content is for informational purposes only and does not substitute for professional medical advice.