What Does the Flu Shot Actually Do? (And Why You Should Get It)

October 28, 2022

Every year we hear and see news reports about the influenza vaccine. They talk about how important it is to get the vaccine, how well the flu vaccine matches the year’s virus, and how effective experts think it will be. So, how important is the matching, what does the flu shot do, and why should you get it?

Scientists develop new vaccines yearly to match the most common circulating influenza strains.

Every year, a new seasonal flu begins circulating in Australia and other countries in the southern hemisphere. Flu viruses constantly evolve and change, which is why we need new vaccines. Scientists examine the circulating strains to find which ones cause the most infections. Based on that information, they develop the vaccines they think will give the most protection. These are the vaccines people in North America get at the start of their flu season – usually in October.

The flu vaccine tricks your body into thinking it had the infection.

There are several types of flu vaccines aimed at helping as many people as possible. Most vaccines contain an inactivated virus, which means the virus is dead. Others have a weakened virus. After the vaccination, your immune system detects a protein on the virus and produces antibodies to fight it. Once the antibodies are present, if you come in contact with the virus again, your immune system protects you because it thinks you already had the virus.

The flu vaccine does not make you sick.

It’s a common myth – that the flu vaccine can give you the flu. This is often based on people becoming ill within days of vaccination. The inactivated and weakened viruses do not give people the flu. But it does take up to two weeks for your body to develop immunity. If you come into contact with the flu virus just before you get your vaccine or within two weeks of getting it, you could still become sick. It wasn’t the vaccine that caused it. It was the exposure to the virus before the vaccine could work.

Flu vaccines aren’t always a good match.

No matter how hard scientists try, they don’t always get a good match for the flu vaccine. This means it’s not as effective as they would like. According to the Mayo Clinic, “Reviews of past studies have found that the flu vaccine is about 50% to 60% effective for healthy adults between 18 and 64 years old. The vaccine may sometimes be less effective.”

That being said, even if the vaccine doesn’t always prevent the flu, having the vaccine can help reduce how sick you would be if you catch the infection. It significantly reduces the chances of hospitalization and death.

Everyone who can get a flu shot should.

Everyone who can get a flu shot should, say experts. The immunizations don’t only protect you from the flu; they protect those around you who may not be able to get vaccinated. These include people who are:

  • Less than six months old
  • Immunocompromised, whose immune system isn’t strong enough to protect them
  • Severely allergic to the vaccine

Some people should only receive certain vaccines, so they should speak with their doctor or nurse practitioner before getting their vaccination. These include people who:

  • Are allergic to eggs
  • Have had Guillain-Barré syndrome
  • Had a severe reaction to a previous vaccine
  • Are not feeling well at the moment

Everyone else, including those who are pregnant, should be vaccinated. The vaccine given during pregnancy helps protect the baby once born, so there is an added benefit.

Even people already in the hospital for other reasons are encouraged to get a flu shot. According to a large study looking at over 30 million hospital records, patients who had a flu vaccine while hospitalized had a 10% lower chance of having a heart attack.

There is a nasal spray vaccine.

Not everyone can tolerate getting an injection because of fear of needles or allergies to eggs or other ingredients in the injected formulations. These people may be candidates for the nasal spray flu vaccine. Unfortunately, it isn’t for everyone though. It’s only approved for people between 2 and 49 years, for example. Please go to the CDC page, Who Should and Should NOT Get a Flu Vaccine, for the complete list.

Influenza can lead to sepsis.

Sepsis is the body’s life-threatening response to infection. Not only can influenza, a viral infection, cause sepsis, it can lead to complications like bacterial pneumonia, which can also cause sepsis.

If you do become sick with the flu, watch for signs of sepsis. Sepsis is a medical emergency. Seek medical help immediately if you believe you may have sepsis.

If you want to learn more about the flu and how it can lead to sepsis, visit Sepsis and Influenza, part of the Sepsis and… library.