A new COVID-19 shot is here, and the Food and Drug Administration is recommending everyone 6 months old and up get it. Infectious disease experts have said the new vaccines , which target the KP.2 variant thats behind the most recent wave of infections, do a better job at preventing serious outcomes like hospitalization and death.

If its been a second since youve gotten a booster shot, then let this serve as a quick reminder that its very normal and common to feel under the weather for a day or two after you get vaccinated, and flu-like symptoms are a sign the shot is doing its job.

These symptoms may be reflective of a more robust immune response to the vaccine, which leads to longer-lasting and stronger protection, Dr. Scott Roberts , a Yale Medicine infectious disease specialist, told HuffPost.

Heres why you may not feel so well after getting the new COVID-19 vaccine.

According to the FDA, the new shots are expected to trigger side effects similar to those of the previous COVID-19 vaccines: headaches, fatigue, mild fevers and muscle pains.

Pain at the injection site is frequently reported, as is a red, itchy rash, which has been nicknamed COVID arm . Some individuals may also experience gastrointestinal issues , like diarrhea and nausea, as well as swollen lymph nodes .

The vaccine essentially tricks the body into responding as if you have an infection. As a result, the side effects of the vaccine or booster can feel like a milder version of a COVID or flu infection when the immune system is stimulated, even though there is no actual infection happening, Dr. Anne Liu , an infectious disease and allergy/immunology specialist with Stanford Medicine, told HuffPost.

The side effects vary from person to person, according to Dr. Amesh Adalja , a senior scholar at the Johns Hopkins Center for Health Security and an infectious disease expert. And if you recently had COVID-19? Well, you might have a stronger reaction since your immune system was recently primed to go after the coronavirus, Adalja said.

Dont worry, most side effects are a sign the vaccine is working.

When the immune system is stimulated, as it is when youre vaccinated, it releases various molecules that trigger symptoms like muscle aches, Adalja said.

These side effects indicate the vaccine is doing its job. One study found that the more post-vaccine side effects you have, the stronger your immune response is. The study also found that experiencing chills, tiredness and headaches after getting one of the COVID-19 vaccines was linked to higher levels of neutralizing antibodies up to six months later.

With that said, many people dont experience any symptoms after getting vaccinated and thats OK, too.

Most people have minimal side effects to the COVID vaccination, but almost all of them form excellent memory responses to the vaccination, Liu said.

Adverse events are uncommon, but they do happen. If you experience chest pain, shortness of breath or an irregular heartbeat, you should seek medical treatment immediately. These symptoms could be due to serious cardiovascular complications, like myocarditis or pericarditis.

These are very rare, and in almost all cases the benefits of the vaccine outweigh the risk of these side effects, Roberts said.