Why do I still get the flu after getting the flu vaccine?

At the beginning of winter, I went to get a flu shot early because I had experienced the severity of the flu. For the health of myself and my family, I never expected that I would get the flu soon after. I had a fever, cough, vomiting, and body aches. I was so uncomfortable that I questioned my life. How could I get the flu after getting the vaccine?

1. The “Master of Face Changing” in the Virus World

The influenza virus is a master of face-changing in the virus world, and it mutates very quickly. Every year when the flu season comes, the virus may change into a different "coat". The development of the influenza vaccine is like "drawing a portrait" of the virus. Scientists prepare the corresponding vaccine in advance based on the influenza virus strains that were prevalent in the previous year. But when the new flu season comes, the virus may have "changed its appearance", and the "portrait" targeted by the original vaccine is not quite matched, which greatly reduces the protective effect of the vaccine.

2. It takes time for immunity to take effect

After the flu vaccine is administered, it does not work in our body immediately. After the vaccine enters the human body, our immune system needs some time to recognize it and produce corresponding antibodies. This process takes about 2 to 4 weeks.

During this period, the human body's immunity has not yet been fully established, just like an army that has not been fully trained and cannot resist foreign invasion. If the flu virus takes advantage of this period, we may be infected. For example, if you have just received the vaccine and accidentally come into contact with a flu patient a few days ago, the virus is likely to "take over" your body before your immune system is ready.

3. The efficacy of the drug varies from person to person

Everyone's physical condition is unique and their responses to vaccines vary. Some people have very strong immune systems and can quickly produce a large number of effective antibodies after vaccination, just like a well-trained and highly combat-capable army that can easily resist the invasion of influenza viruses. However, some people have relatively weak immune systems, such as the elderly, children, or people with chronic diseases. They may produce fewer antibodies after vaccination, or the quality of the antibodies may be low, which makes the vaccine's protection less than expected.

Although the flu vaccine can prevent most common flu viruses, it is not a panacea and cannot guarantee that we are immune to all flu viruses. The influenza virus family is huge. In addition to the several major strains targeted by the vaccine, there are many other subtypes and variants. Therefore, even if you have received the flu vaccine, you cannot completely relax your vigilance and ignore daily protective measures.

Lin Chen, head nurse of the adult emergency department of the Second Affiliated Hospital of Wenzhou Medical University