Flu Shot: How It Works, Duration, And Side Effects

Feb 01 2018

Flu Shot: How It Works, Duration, And Side Effects

The flu shot is the medicine of choice to fight against the influenza virus. Flu is a serious virus that leads to many illnesses and even deaths, each year. You don’t have to be young or have a compromised immune system to get ill from the infection. Healthy people can get sick from the flu and spread it to friends and family.  Flu-related deaths are most common in seniors age 65+.

The best and most efficient way to avoid the flu and prevent spreading it is to get vaccinated. The flu vaccine is available as an injectable shot. The more people vaccinated against the flu, the less the flu can spread.

This vaccine, which typically comes as a shot but also as a nasal spray, can reduce your chances of getting the flu by as much as 60 percent.



flu shot

Flu Shot: How Does It Work?

To make the vaccine, scientists select the strains of the flu virus that research suggests will be the most common in the coming flu season. Millions of vaccines with those strains are produced and distributed.

Once you receive the vaccine your body begins producing antibodies against those strains of the virus. These antibodies provide protection against the virus. If you come into contact with the flu virus at a later point, you have a better chance to avoid an infection. However, you can still get sick if you contract a different strain of the flu virus.  But the symptoms will be less severe because you are vaccinated.



Flu Shot: Who Gets Vaccinated?

Doctors recommend that everyone over the age of 6 months receive the flu vaccine.

This is especially true for people in high-risk categories, such as:

  • seniors over age 65 who tend to have weak immune systems
  • pregnant women
  • children under age 5
  • people, regardless of age,  with weakened immune systems due to chronic illness

Most doctors also recommend everyone gets their flu vaccine by the end of October. This way your body has time to develop the right antibodies before flu season kicks into gear. It takes about two weeks for antibodies to develop against the flu after you get the shot.


Flu Shot: Duration?

Most people will recover from the flu in about one week. But it may take several more days for you to feel back to your usual self. It’s not uncommon for you to feel tired for several days after your flu symptoms have subsided.

It’s important you stay home from school or work until you haven’t had a fever for at least 24 hours. This is without taking fever-reducing medications. If you have the flu, you’re contagious a day before your symptoms appear and up to five to seven days afterward.


Flu Shot: Side Effects

Many people report avoiding the flu vaccine each year for fear that it will make them sick. It’s important to understand that the flu vaccine can’t cause you to develop the flu. You aren’t going to become sick because you received the vaccine.

Flu vaccines contain dead or weakened strains of the flu virus. These strains aren’t strong enough to cause an illness.

You may experience some side effects from the flu shot. These side effects are often mild and only last a short period of time. The side effects of a shot outweigh the possible symptoms of a flu infection later.

The most common side effects of the flu shot include:

  • soreness around the flu shot injection site
  • low-grade fever in the days immediately following the injection
  • mild aches and stiffness
  • low grade temperature

Any side effects that do occur often only last a day or two. Many people won’t experience any side effects.

On rare occasions, some people may have a serious allergic reaction to the vaccination. If you’ve had an allergic reaction to any vaccine or medication before, talk with your doctor first.


Most Common Flu Shot Side Effects

The most common side effect of the flu shot is a reaction at the injection site, which is typically on the upper arm. After the shot is administered, you may have soreness, redness, warmth, and in some cases, slight swelling. These effects usually last less than two days. To help reduce discomfort, try taking some ibuprofen before getting your shot.

After your shot, you might have headaches or some achiness and pain in the muscles throughout your body. This also usually happens on the first day and goes away within two days. Taking pain relievers such as ibuprofen can help ease your discomfort.

Some people experience dizziness or fainting with the flu shot. These effects should not last longer than a day or two. If you tend to get dizzy or faint when getting a shot, be sure to tell your doctor immediately. Try a light snack and orange juice.

A fever of 101°F or less is a common side effect of the shot. A slight fever is considered a mild side effect, and it should go away within a day or two. If the fever bothers you, you can take ibuprofen or acetaminophen.


Flu Vaccine In A Nasal Spray

Like the flu shot, the flu nasal spray (also called the LAIV, or live attenuated influenza vaccine) may cause headache, slight fever, dizziness, and fainting. However, the nasal spray can also cause other side effects that the shot does not, including tiredness, loss of appetite, runny nose, and sore throat.

Please note, the nasal spray is not available every year. Always heck the CDC website (Center For Diseases Control) for more information.

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Barry G

Barry graduated from City University of New York and holds a Ph.D. in Physiological Psychology.

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