Influenza Vaccine: When Is the Flu Vaccine Given and Who Is It Recommended For?

The influenza vaccine is given to protect against seasonal flu and the serious complications flu can cause. It comes up again every year both because flu viruses change and because the immunity produced by the vaccine wanes over time. In this article I explain the timing of the flu vaccine, who it is particularly important for, and its use in pregnancy.

When answering “I had the vaccine last year but still got sick; should I get it this year?”, two points need to be separated: not every respiratory infection is flu, and the benefit of the flu vaccine is not limited to preventing infection. The vaccine can also reduce the risk of severe illness and hospitalisation.

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What is influenza?

Influenza is a contagious respiratory illness caused by flu viruses. It usually presents with sudden weakness, muscle aches, headache, cough and fever. However, not every person with flu has a fever.

What is the difference between flu and the common cold?

In a cold, a runny nose, sneezing and throat complaints may be more prominent. Flu, on the other hand, can affect a person so much that they cannot carry out daily activities. Because the symptoms can be similar, it is not always possible to distinguish them with certainty based on symptoms alone.

In some people flu can lead to pneumonia or trigger a worsening of existing conditions such as asthma and heart disease. ^[1]

What is the flu vaccine?

Flu vaccines are prepared to build immunity against the influenza viruses expected to circulate. Because the viruses change, the vaccine composition is reviewed regularly.

The second reason for annual vaccination is that the protection from the previous vaccine decreases over time. Having been vaccinated last season does not mean you are protected to the same degree in the new season.

When deciding on vaccination, a product prepared for that season and suited to the person’s age and health status should be chosen. “Influenza vaccine” is not a single brand name but a general term for flu vaccines. ^[2]

Who is the flu vaccine recommended for?

With rare exceptions, the CDC recommends a flu vaccine every season for everyone aged 6 months and older. Vaccination is particularly important for people at high risk of severe illness. ^[3]

Risk groups also highlighted by the Turkish Ministry of Health include:

• Older adults
• Pregnant women
• Young children
• People with chronic heart, lung, kidney or metabolic disease
• People with diabetes
• Immunocompromised people
• People living in communal settings such as care homes

Being in a risk group does not mean a person will necessarily become seriously ill if they catch flu. However, it makes protection more important. ^[4]

When should you get the flu vaccine?

For most people, September and October are a suitable time to get vaccinated before the flu season. It takes about two weeks after vaccination for a protective immune response to develop.

However, not having been vaccinated in autumn does not mean the vaccine can no longer be given in winter. As long as flu viruses continue to circulate, vaccination can be beneficial. Timing should be determined taking into account the person’s age, pregnancy status and previous vaccines. ^{[2, 3]}

Can the flu vaccine be given during pregnancy?

Flu during pregnancy can increase the risk of illness requiring hospitalisation. For this reason, pregnancy is not a general reason to postpone the flu vaccine; on the contrary, it is one of the times when vaccination is particularly important.

Inactivated flu vaccines suitable for pregnancy can be given in any trimester of pregnancy. There is no need to wait until the first three months are over. The live flu vaccine given through the nose, however, is not used in pregnancy.

As an obstetrician and gynaecologist, I place particular importance on this: in pregnancy care, assessing vaccination needs — not just tests and ultrasounds — is part of preventive care. ^[5]

Does a flu vaccine given in pregnancy also protect the baby?

Antibodies produced during pregnancy pass to the baby and can help protect it from flu in the first months after birth. This is valuable for babies who are too young to receive their own flu vaccine.

This protection is neither complete nor unlimited. Nevertheless, vaccinating the mother-to-be can contribute to both the mother’s health and the baby’s early protection. ^[5]

How many doses of the flu vaccine are given?

In adults, the flu vaccine is usually given as a single dose each season. In children, the number and timing of previous flu vaccines matter.

Some children need two doses at least four weeks apart in the same season. For this reason, the schedule should be planned in advance, especially for children receiving the flu vaccine for the first time. The flu vaccine is not given to babies younger than six months. ^[3]

How well does the flu vaccine protect?

The effectiveness of the flu vaccine is not the same every season. The match between circulating viruses and the vaccine, the person’s age and immune system all affect the outcome.

In seasons when the viruses are well matched, the risk of needing to see a doctor because of flu can be reduced by about 40–60%. A vaccinated person can still get flu; nevertheless, vaccination can reduce the risk of severe illness and hospitalisation.

For this reason, judging the vaccine only by the question “did I not get sick at all that winter?” gives an incomplete picture. ^[6]

What are the side effects of the flu vaccine? Can the vaccine give you flu?

The injectable inactivated flu vaccine does not cause flu. Arm pain, a mild fever or tiredness after vaccination are not the same as a flu infection.

The most common side effects are pain and redness at the injection site, headache, muscle aches and fatigue. They usually resolve quickly. If a serious allergic reaction occurred after a previous flu vaccine, a separate assessment is needed before vaccination. ^[5]

Frequently asked questions about the flu vaccine