How the flu shot works—and why you should get yours

General Wellness
Young woman with rolled sleeve for flu shot

In the past few years, many people have learned a lot about viruses and other infectious diseases. From how they spread to how to prevent them, COVID-19 has led many to understand how to stay healthy and protect themselves from getting sick.

This knowledge doesn't just apply to COVID-19. It also helps you stay safe from an older (but certainly not forgotten) illness—the flu.

The flu, or influenza, has been around for at least a century. While the exact origin of the virus is not known, it led to its own pandemic in 1918. Today, strains of the flu virus linger, causing a contagious respiratory illness that impacts your nose, throat, and lungs. While the flu may sometimes be minor, it can also be serious, leading to hospitalization and even death.


Between 2010 and 2020, each year, the flu led to an estimated:

  • 9 to 41 million illnesses
  • 140,000 to 710,000 hospitalizations
  • 12,000 to 52,000 deaths

According to Amy Schultz, DO, primary care provider at Main Line Health, "Fortunately, there are plenty of known ways to protect yourself against the seasonal flu. These include washing your hands frequently, avoiding people who are sick, and getting your yearly flu vaccine."

The flu shot is one of the most important ways to avoid getting the flu. Here's an overview of how this vaccine works and why you should get yours this flu season (and every flu season).

How does the flu shot work?

Like many vaccines, the flu shot works by causing your body to create antibodies against the flu. These antibodies protect against future infection, making it easier to fight off the illness if you become exposed.

"A common misconception is that the flu vaccine causes the flu. This is not true," explains Dr. Schultz. "Instead, the injected version of the vaccine (the flu shot) is either made with inactivated (or killed) viruses, or one single protein from the flu virus. The nasal spray flu vaccine is made with weakened viruses that can't cause illness."

Every year, the strains—or types—that cause the seasonal flu are different, and researchers work hard to predict which they believe will be the four most common strains. These go into that year's flu vaccine, so getting your flu vaccine each year becomes even more essential.

The flu vaccine's effectiveness depends on the season, including whether or not the strains in the vaccine were well-matched to the ones that spread. When this match is strong, studies have shown that the flu vaccine reduces your chances of getting sick by up to 60%. From 2019 to 2020, the vaccine prevented an estimated 7.5 million cases of the flu.

Why you should get your flu vaccine

During the flu pandemic of 1918, there was no flu vaccine to protect against getting sick. Because of this and a lack of treatment options, roughly one-third of the world became infected with that flu virus.

In the past 100 years, we've come a long way in preventing illnesses, including the flu. With modern medicine, you have the ability not just to avoid getting sick—but also to protect others around you.

The flu vaccine can:

  • Keep you from getting the flu. This can mean anything from fewer missed days at work to a reduced chance of ending up in the hospital to saving your life.
  • Make your illness less severe if you do get sick.
  • Protect others around you, including those who are more likely to get severely sick from the flu, such as babies, older people, and people with chronic conditions.
  • Reduce your chances of flu-related complications if you have a chronic condition, such as heart disease, lung disease, or diabetes.
  • Lower the risk of flu-related complications in pregnant women and help protect the baby for several months after they're born (if the mom is vaccinated during pregnancy).

Protecting yourself and others this flu season

Getting sick with the flu can range from being inconvenient to deadly. Fortunately, thanks to the research and dedication of flu experts, the flu vaccine can reduce your risk of getting the flu and spreading it to others.

The flu shot takes just a few minutes of your time each year. As one of the most important protective measures against the flu, it can go a long way in keeping you and your loved ones healthy this flu season—and every flu season in the future.

Register for an upcoming flu shot clinic

Main Line Health serves patients at hospitals and health centers throughout the western suburbs of Philadelphia. To schedule an appointment with a specialist at Main Line Health, call 1.866.CALL.MLH (225.5654).