Why do you think the flu vaccine is recommended every year? How does the vaccine affect the immune system?
When is the best time to get a flu vaccine? Why?
Is the vaccine effective?
Who is and who is not recommended to receive a flu vaccine? Why do these recommendations exist?
Why is it important for the CDC to update its flu vaccination recommendations each year?

I'll answer what i can

Its recommended because it can help fight the flu if you get it

It affects the immune system by training it to target the flu, and gain resistance to it

The best time is during cold, due to the fact that cold helps the virus (heat kills some viruses)

depending on the person depends on whether its effective or not.

Its important for the CDC to update it every year because the flu isn't always the same, and can adapt to the shot to where it has no effect.

full answer for plato/gradpoint :) its 100% correct it was my answer

Explanation:

Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses. When you get vaccinated, your immune system produces antibodies to protect you from the viruses included in the vaccine. But antibody levels may decline over time — another reason to get a flu shot every year.

Getting a flu vaccine prepares your immune system for the flu. A flu vaccine teaches your immune system to recognize that virus as a threat. While some people may still get the flu after having a flu shot, they'll probably have a milder form of the illness. That's because antibodies made in response to the vaccine can still provide some protection.

The flu virus is around all year, but it spreads more easily from September through the spring, generally peaking between December and February. It takes about 2 weeks to develop enough antibodies from the flu vaccine to protect you against the flu. Protection fades over time, so getting vaccinated before September may leave you more vulnerable toward the end of flu season. You can continue to get the vaccine through late winter to early spring.

How well the flu vaccine works (or its ability to prevent flu illness) can vary from season to season. The vaccine’s effectiveness also can vary depending on who is being vaccinated.

People who can get the flu shot: Different flu shots are approved for people of different ages. Everyone should get a vaccine that is appropriate for their age. There are inactivated influenza vaccines (IIV) that are approved for people as young as 6 months of age. Pregnant women and people with certain chronic health conditions can get a flu shot.

People who should not get the flu shot: Children younger than 6 months of age are too young to get a flu shot. People with severe, life-threatening allergies to flu vaccine or any ingredient in the vaccine. This might include gelatin, antibiotics, or other ingredients.

These recommendations exist for the safety of people having different health conditions.

Every year the flu season is different, and influenza infection can affect people differently, but millions of people get flu every year, hundreds of thousands of people are hospitalized and thousands to tens of thousands of people die from flu-related causes every year. An annual seasonal flu vaccine is the best way to help protect against flu.