Flu Vaccination 101: How Long Does a Flu Shot Last and How Effective Is It?

The flu shot is the best and most effective method of prevention against influenza infections. It is commonly administered on an annual basis, and its composition can vary from season to season.

How long does a flu shot last? Though administered once a year, it offers up to six months of effective protection. October is the month when most patients receive their flu shots.

Keep reading to find out more on how the flu shot works, how it’s made, when to get it, and who should get it.

Why Should You Get the Flu Shot?

In short, a flu shot significantly decreases your chances of contracting the flu. This is especially important for older people, children, and those with compromised immune systems.

While you can still get the flu after the shot, your body will have developed enough antibodies to stave off most of the mild and intermediate infections.

According to the Centers for Disease Control and Prevention (CDC), between 140,000 and 710,000 people get hospitalized every year due to influenza and influenza-related health problems.

How Do Flu Shots Work?

Flu shots contain small amounts of the virus strains they are supposed to protect you against. These quantities are too low to actually cause you to get sick, but are high enough to alarm your immune system and get it working.

When you get the flu shot, it takes around 14 days for it to start working. In those two weeks, your body will develop the necessary antibodies to kill the viruses present in the vaccine. Those antibodies will then continue to protect you from the infections throughout the season.

Have in mind that you can still catch the flu during the incubation period, so pay extra attention to the hygiene. Also, try to avoid big crowds or visiting someone who might have the flu. On top of that, be careful not to touch your mouth or nose with your hands, especially if you haven’t washed them thoroughly.

How Effective Are Flu Shots?

The efficacy of a flu shot depends on how well the strains it contains match the influenza strains that year. When the match is good, the shot can reduce your chance of getting the flu by 60%. On the other hand, a poor match might leave you less protected.

Seasonal influenza shots are not a guarantee that you won’t get sick during the flu season. They can’t protect you from stomach viruses, bacterial infections, or other illnesses typical of the flu season. That’s because they are not caused by the influenza virus. Flu shots can only protect you from influenza viruses they contain.

How Long Do Flu Shots Last?

Well, how long does a flu shot last? In a nutshell, the shot lasts one season. The mix of strains included in the shot one year might differ from the mix of strains included the previous or the next year. This is due to the fact that the influenza virus strains are constantly changing and evolving.

Therefore, the shot that effectively protected you the last season might not protect you that well this season. Generally, the changes and variations are not drastic from season to season. However, to be on the safe side, it is important to get a shot every year.

Each year, experts work hard to determine the most likely strains to cause epidemics that season. Once the research is done, they choose the top three or four strains and put them into the vaccine. Most commonly, the seasonal shot will contain two influenza A strains and one or two influenza B strains.

When Should You Get the Shot?

Typically, healthcare providers will receive the first flu shot shipments as early as August. Most manufacturers will ship their shots by September.

Though it is easy to go with the “the earlier the better” rule here, there is some evidence that it might not be good to get the shot that early. A study published in 2017 found that the level of protection decreases each month after receiving the shot. Therefore, if you take the shot in August, you might be far more susceptible to catching the flu in February or March.

The CDC recommends getting the shot in October, before the flu season revs up. It is also OK to get the shot later, as the flu season might extend all the way to March.

What Are the Side Effects of Flu Shots?

Like any other drug or medical treatment, the flu shot can cause a range of side effects. People often don’t experience any of them. Even if they do, these side effects tend to be very mild in most cases. The most common ones include:

  • Injection site reaction. Some people may experience soreness, redness, or swelling at the injection site. These symptoms usually go away on their own in a day or two.
  • Pain and headache. You may also feel headache and muscle or joint pains after you’ve received the shot. Commonly, the symptoms should go away in a day or two.
  • Fainting and dizziness. If you get dizzy or feel as if you’re about to faint, sit down and wait for the feeling to pass. It is also a good idea to snack on something.
  • Slight fever (101 degree Fahrenheit or lower) is a common side effect of a flu shot. It should be gone in a day or two. If you get a high fever, go to a doctor.
  • Allergic reaction. This is a rare side effect. The symptoms might include weakness, dizziness, tachycardia, trouble breathing, swelling, and hives. If you notice any of the symptoms, go to the doctor immediately.

Who Should and Who Shouldn’t Get Flu Shots?

As a rule, everyone 6 months or older should be vaccinated every year. The risk groups include elderly people (aged 65 and older), children 5 years old and younger, pregnant women, and people suffering from conditions such as cancer or asthma.

Babies younger than 6 months should not receive the flu shot as their immune systems can’t cope with the amount of the virus in the vaccine. Instead, all adults and children around them should be vaccinated, thus maintaining herd immunity until the baby is old enough to get the flu shot.

Those suffering from acute illnesses should wait until they’re better to get the shot. In the meantime, they should take extra care to avoid getting infected.

If you currently have or have previously had any of the following conditions, you should tell your doctor before getting the shot:

  • Guillain-Barre syndrome
  • Previous vaccine complications
  • Severe allergies

Final Words

A flu shot is prepared for each flu season and includes the influenza virus strains that will most likely be prominent the following season. A well-made shot can decrease your chances of contracting the flu by up to 60%.

The shot lasts for one season. If you take it in August when it first becomes available, you might be more vulnerable in the late stages of the season than someone who received theirs in October. Mild side effects are common and tend to go away in a day or two. However, if you notice high fever or an allergic reaction, call your doctor as soon as possible.