[Medical Q&A] Why do children still get infected even though they get the flu vaccine every year?

Planner: Chinese Medical Association

Reviewer: Niu Chao, deputy chief physician, Children's Hospital Affiliated to Chongqing Medical University

Flu vaccine is a biological product. Its main function is to stimulate the human immune system to produce antibodies against flu viruses, thereby enhancing the body's resistance to flu viruses, reducing the risk of flu infection or alleviating flu symptoms. Many parents choose to vaccinate their children with flu vaccines in the hope of preventing flu. However, some parents have found that even if they vaccinate their children with flu vaccines every year, their children may still get the flu. Why is this?

First, influenza viruses have the property of mutation. Influenza viruses are highly variable, and the strains circulating each year may be different. Vaccine development and production take a certain amount of time, and during this time, the influenza virus may have mutated. Therefore, even if the vaccine can provide effective protection against last year's virus strains, it may not be able to completely protect against this year's new virus strains.

Secondly, the protective effect of the vaccine is not 100%. The protection rate of influenza vaccines is usually between 70% and 90%, which means that even if you are vaccinated, there is still a certain probability of contracting influenza. In addition, the protective effect of the vaccine is also affected by individual differences. For example, the immune system of the elderly is relatively weak, and their response to the vaccine may not be as strong as that of young people. Similarly, children may not respond strongly to the vaccine because their immune system is not yet fully mature.

Thirdly, it takes time for antibodies to develop after a flu shot. Generally speaking, it takes 2 to 4 weeks after a shot for the body to produce enough antibodies to fight the flu virus. If a child is exposed to the flu virus before antibodies are produced, they may be infected with the flu. In addition, antibodies are usually effective for 8 to 12 months, so even if a child was vaccinated last year, this year's antibody levels may have dropped and not provide adequate protection.

Although it is still possible to get the flu after getting the flu vaccine, it does not mean that the vaccination is meaningless. A large number of studies have shown that getting the flu vaccine can significantly reduce the risk of children getting the flu. Even if they are unfortunately infected, it can reduce the severity of symptoms and reduce the probability of complications such as pneumonia and otitis media. Therefore, giving children the flu vaccine on time every year is still one of the most effective ways to prevent the flu.

In short, influenza vaccination is an effective measure to prevent influenza, which helps the body resist the invasion of influenza viruses by stimulating the immune system to produce antibodies. It is recommended to get the influenza vaccine every year, especially for high-risk groups, to reduce the risk of influenza infection and related complications.