Frequently asked questions about flu vaccination

Seasonal flu is an acute respiratory infection caused by influenza virus. The disease is transmitted directly from sick people to healthy people through small droplets when talking, coughing, sneezing. In Vietnam, the common viruses that cause seasonal flu are Influenza A/H3N2, A/H1N1 and Influenza B.

Seasonal influenza is usually benign, but can also cause serious and dangerous complications in people with chronic cardiovascular and respiratory diseases, people with immunodeficiency, the elderly, children and pregnant women. The disease can cause severe pneumonia, multiple organ failure leading to death.

Flu vaccination is the most effective way to prevent the disease and avoid serious complications. Below are some answers to common questions parents have about seasonal flu vaccines, according to nurse Ha Thi Thanh Hoa, Department of Infection Prevention and Control, National Children's Hospital.

What strains of flu can the flu vaccine prevent?

Vietnam is currently using four types of influenza vaccines: Influvac Tetra (Netherlands), GC Flu Quadrivalent (Korea), Ivacflu-S (Vietnam) and Vaxigrip tetra (France). Of these, three foreign vaccines protect against four strains of influenza, including two strains of influenza A and two strains of influenza B.

How long does it take for the flu vaccine to be effective and can you still get sick after getting vaccinated?

About 4 weeks after getting the flu vaccine, your body can form the highest level of antibodies that protect you from the flu virus strains in the vaccine.

After vaccination, it is still possible to get sick due to a number of reasons such as the vaccine's duration of action is not long enough, catching a flu strain that is not prevented by the vaccine; the body cannot respond to the immune system for the flu vaccine; not getting a booster shot every year. However, most people who get the flu after getting enough doses of the vaccine will have milder symptoms and a lower rate of complications compared to those who have not been vaccinated.

A baby receives a vaccine injection at the National Children's Hospital. Photo: Giang Huy

Who should get a flu shot?

All children 6 months of age and older and those who are at risk of influenza should be vaccinated. In particular, people at high risk of complications are encouraged to be vaccinated as soon as possible, including: people over 65 years of age; women who are pregnant or planning to become pregnant; children from 6 months to 5 years of age; people with chronic diseases such as asthma, diabetes, cardiovascular disease, cancer, kidney failure; people with immunodeficiency, and people who have direct contact with people in high-risk groups for influenza.

Do I need to get vaccinated again after recovering from the flu?

There are many strains of the flu virus, and they are always changing. So, even if you have just recovered from the flu, you should still get vaccinated.

Can I get the flu vaccine while pregnant?

Flu vaccines can be given before and during pregnancy. Flu vaccination for pregnant women has a double benefit as it can protect both mother and fetus. When vaccinated, antibodies produced in the mother's body are passed to the fetus, these antibodies will protect the baby from flu until the baby can get the first flu vaccine at 6 months of age.

What is the flu vaccination schedule?

Children from 6 months to under 9 months who have not been previously vaccinated: 2 doses at least 4 weeks apart. Then a booster dose every year.

Children 9 years of age and older and adults: One dose and a booster dose annually.

Why do we need to get a flu vaccine booster every year?

There are many strains of influenza viruses, and strains are always changing. Therefore, antibodies produced in response to a vaccine may be effective one year but may not be effective against influenza viruses the following year. The components of the influenza vaccine are researched, updated, and changed each year to better match the strains of influenza viruses circulating that year. Therefore, influenza vaccination should be repeated each year.

Micah Soto

Update 18 February 2025