Flu Vaccine Questions Answered: How Vaccines Work, Side Effects and More

Every fall, we hear frequent reminders to get a flu shot for protection against the influenza virus. While flu shots have been widely available since the 1940s, there are still questions, myths and common misconceptions about the vaccine.

In this article, John Adams, MD, a board-certified infectious disease physician at Covenant Health, answers flu vaccination questions and provides the latest best practices to help you stay healthy throughout this year’s flu season and beyond. 

How Does the Flu Shot Work? 

The Centers for Disease Control and Prevention explains that vaccines can either contain inactivated virus which are no longer infectious, or a particle designed to look like an influenza virus to your immune system. 

“The influenza vaccine is developed six to nine months in advance by healthcare professionals and is anywhere from 40 to 60 percent effective,” Dr. Adams said. “The makeup of the influenza vaccine is adjusted annually for expected prevalence of disease. Protection lasts in your body for an average of six to seven months from inoculation. The injectable vaccine contains no live virus, so one cannot get influenza from the vaccine.” 

Who Should Get the Flu Vaccine? 

“All adults should get an annual flu shot. Annual flu shots are also recommended for children ages 6 months and older,” said Dr. Adams. “You can always ask your healthcare provider if you have questions on timing and eligibility.” 

Why Should I Get the Flu Shot? 

Dr. Adams encourages everyone to get the flu shot to prevent illness. “Healthy individuals can still get sick from the flu and COVID,” he said. “The flu shot will protect you from both A and B strains of influenza. It’s like wearing your seatbelt – it’s a simple precaution that protects you in case of an accident. If you don’t get in an accident, then you may not have needed its protection. However, if you are in a car accident, the injuries are likely to be much worse if you are not wearing a seatbelt. Like a seatbelt, vaccines protect you from a worse outcome.”

When is the Best Time to Get the Flu Vaccine? 

“The recommended time to get a flu shot is late September to early October. It’s important to get it sooner than later, as it takes about two weeks to take effect,” Dr. Adams said. “Influenza vaccines are designed to combat the newest strain of the virus each year. As disease begins to spread later in the fall and winter, your body will have had time to build up antibodies to keep you from getting sick if the case you are exposed to the flu.” He noted that the vaccine will provide protection for up to a year.

Why Do I Need a Flu Shot Every Year? 

On average, eight percent of the United States get sick from flu each flu season, which lasts roughly October to April, with peaks in December and February. Flu viruses continually change, and the flu vaccine is updated annually in anticipation of those changes. Additionally, your immune protection decreases over time.

To protect yourself from the flu, it’s best to receive an annual vaccination. Knowing tips to avoid the flu, like washing your hands often, is an additional way to protect yourself from illness.

Common Flu Shot Side Effects – What to Expect 

Dr. Adams notes that with any medication, there is always a possibility of risk, including side effects. However, he stressed that possible side effects of vaccines such as fever, fatigue or allergic reaction, are rare and infrequent. According to the CDC, side effects like soreness, redness and/or swelling can occur at the injection site. Additionally, you may experience a headache, nausea and muscle aches. 

“Everything we do has potential risks, and these are calculable and known,” Dr. Adams said.” The vaccine is extremely safe, with serious side effects reported only rarely.”

Can a Flu Shot Make Me Sick? 

Despite what you may hear, Dr. Adams affirms you cannot get sick from a flu shot. “The injectable vaccine contains no live virus, so you cannot get influenza from the vaccine.” If you do feel like you have cold or flu symptoms after receiving a vaccine, it is your immune system at work, building a stronger immune response. 

Rare allergic reactions or Guillain-Barré Syndrome may occur. However, the risk of allergic reactions or GBS are only one to two cases per one million doses of flu vaccine administered.  

How to Relieve Side Effects From the Flu Shot 

Most side effects from the flu can be treated with over-the-counter pain relievers like acetaminophen or ibuprofen. If you experience more serious side effects or suspect you’re having an allergic reaction, seek immediate medical attention by visiting the nearest emergency room or calling 911. 

How Long Do Flu Shot Symptoms Last? 

Symptoms from the flu shot such as soreness or swelling at the injection site typically go away anywhere between a few hours and a few days. 

Can I Still Get the Flu Even if I Received a Flu Shot? 

Yes, it’s possible to get the flu even if you got your flu shot. The CDC says this can happen for a few reasons. For example, you may be exposed shortly before or after getting vaccinated. It takes roughly two weeks until the vaccine begins to protect you, so exposure close to the time of the shot can still cause you to get sick.

Another reason is that you may have a type of flu virus not protected by the vaccine. Multiple flu viruses exist, and the shots protect against those that research suggests will be most common. You can also get a type of flu that the shot is supposed to deter, but protection varies from person to person based on individual health factors. 

The flu vaccine remains the best way to protect yourself. If you do get the flu, the vaccine continues to provide protection and can reduce the severity of the illness.

If you do become sick from flu or other contagious illnesses, you should prevent the spread by staying home and contacting your health care provider for a treatment plan.  

Where to Get the Flu Shot 

Dr. Adams encourages everyone to get a flu shot, and Covenant Health can help. 

“Covenant Health and its providers are here to care for your family. You can get any of the recommended inoculations, including a flu shot, from a Covenant Health family medicine practice near you,” he said.

“If you have questions about your own health status, ask your provider. We recommend establishing care with your family medicine provider so they can provide annual checkups and immunizations as needed, and will understand your health history to best advise you in case of sickness.”