Influenza vaccine

A flu shot helps you stay well.

It fights a bad bug. This bug can make you sick. The shot helps your body stay strong.

Flu bugs change very fast. Because they change, we need new shots every year. This helps the shot match the new bugs.

Some shots are given in the arm. Other shots are sprayed into the nose.

This is a way to get the shot.

Your body needs two weeks to get ready. After that, it can fight the bug. This helps keep you from getting very sick.

Getting a shot is a good way to stay healthy. It can even help your heart stay strong.

A flu vaccine helps protect you from the flu. The flu is caused by influenza viruses. These viruses change very quickly. Scientists call this change antigenic drift. Because the virus changes, we need new vaccines every year.

There are different ways to get a vaccine. Some are injected into a muscle. This is called an intramuscular shot. Other types are sprayed into the nose. This is called an intranasal spray.

Some vaccines use weakened viruses. Other vaccines use inactive viruses. Inactive means the virus is not alive.

It takes about two weeks for your body to work. During this time, your body makes antibodies. Antibodies are tiny parts that fight the virus. The vaccine helps your body get ready. Even if you get sick, the vaccine can make the illness less severe. It can also help protect your heart.

An influenza vaccine helps protect people from the flu. This illness is caused by influenza viruses. These viruses change very quickly through a process called antigenic drift. This means a tiny mutation happens, and a new strain arises. Because the virus changes so fast, scientists must develop new versions twice a year.

Most vaccines provide modest to high protection against the virus. They can even reduce how sick you feel if you catch a strain not in the vaccine. It takes about two weeks for your body to form protective antibodies after you get the shot.

There are a few different ways a vaccine works. Some vaccines use inactive viruses, which means the virus is not alive. Other vaccines use weakened viral forms.

You can receive these in different ways. Some are injected into a muscle, which is called an intramuscular injection. Others are sprayed into the nose, known as an intranasal spray. Some can even be injected into the middle layer of the skin, called an intradermal injection.

People have been working on these vaccines for a long time. During the Spanish flu pandemic in 1918, doctors tried many things to help patients. In 1931, Ernest William Goodpasture and his colleagues at Vanderbilt University found a way to grow viruses in hen's eggs. Other workers like Thomas Francis, Jonas Salk, Wilson Smith, and Macfarlane Burnet used this to make the first experimental vaccines. By the 1940s, the US military developed the first approved inactivated vaccines for use during World War II.

Science has continued to improve how we make these medicines. In 2012, the US Food and Drug Administration approved vaccines grown in cell cultures. In 2013, they approved vaccines made from recombinant proteins. Many vaccines are now quadrivalent, meaning they target four different lineages of the virus.

For example, the FDA approved Fluzone High-Dose Quadrivalent in November 2019. In 2024, the FDA even recommended removing one specific lineage called B/Yamagata from vaccines. This is because that strain might have become extinct during the COVID-19 pandemic.

Getting a flu shot is a way to stay healthy and help others. The CDC recommends yearly vaccination for almost everyone over six months old. This is especially important for high-risk groups like pregnant women, the elderly, and young children.

Even though side effects like a sore arm or a fever can happen, the vaccine is generally safe. One study even found that a flu shot was as effective or better at preventing heart attacks than quitting smoking. By getting vaccinated, you help stop the spread of the virus to your community.

Influenza vaccines are essential medical tools used to protect people from infection by influenza viruses. These viruses cause the flu, a respiratory illness that can range from mild to severe. Because the virus undergoes a process called antigenic drift, it changes its structure through small mutations. This constant change means that new vaccine versions must be developed twice a year to match the circulating strains. Most vaccines provide modest to high protection against the disease. Even if a person catches a strain not covered by the vaccine, the shot can reduce the severity of the illness.

To work effectively, the vaccine triggers the body to create protective antibodies. This biological process takes about two weeks to complete following vaccination. There are several ways these vaccines are administered to patients. Some are inactivated, meaning the virus is not alive, while others use weakened viral forms. These can be given as an intramuscular injection into a muscle or an intradermal injection into the middle layer of the skin. Another method is the intranasal spray, which is applied into the nose.

The history of influenza vaccination is a journey of scientific discovery. During the 1918 Spanish flu pandemic, medical professionals tried many treatments, including oxygen and blood transfusions. A major breakthrough occurred in 1931 when Ernest William Goodpasture and his colleagues at Vanderbilt University reported that viruses could grow in embryonated hens' eggs.

This method was expanded by scientists like Thomas Francis, Jonas Salk, Wilson Smith, and Macfarlane Burnet to create the first experimental vaccines. By the 1940s, the US military had developed the first approved inactivated vaccines for use during World War II.

Manufacturing technology has evolved significantly since the 1950s when egg-based production became common. In 2012, the US Food and Drug Administration (FDA) approved vaccines grown in cell cultures. In 2013, they approved vaccines made from recombinant proteins. Many modern vaccines are now quadrivalent, meaning they target four different lineages of the virus. However, the composition of these vaccines changes over time. For example, the B/Yamagata lineage of influenza B may have become extinct due to COVID-19 pandemic measures. Because no natural cases were confirmed after March 2020, the FDA recommended removing B/Yamagata from vaccines for the 2024–2025 season.

Vaccine effectiveness is measured in two ways: efficacy and effectiveness. Efficacy is how well a vaccine works under controlled conditions, while effectiveness is how it performs in the real world. Real-world studies are difficult because influenza-like illnesses are often confused with the actual flu. On average, the efficacy against symptomatic disease is between 40% and 60%. Effectiveness can vary greatly by year. For instance, in the 2004 US season, effectiveness was 10%, but it reached 60% in 2010. In the 2019–2020 US season, effectiveness was 41% overall and 54% for people aged 65 or older.

Public health organizations provide specific recommendations for who should receive the vaccine. The World Health Organization and the US Centers for Disease Control and Prevention (CDC) recommend yearly vaccination for nearly all people over six months old. This is especially important for high-risk groups. These groups include pregnant women, the elderly, children between six months and five years, and people with certain health problems. The European Centre for Disease Prevention and Control (ECDC) also emphasizes yearly shots for these high-risk populations. Vaccination in school-age children can also provide indirect protection for other age groups in the community.

While vaccines are generally safe, they can have side effects. Common reactions include soreness at the injection site, fever, tiredness, or temporary muscle pains. In children, fever occurs in about five to ten percent of those vaccinated. In certain years, a link was found between the vaccine and an increase in Guillain–Barré syndrome among older people, occurring at a rate of about one case per million doses. However, the vaccine is considered highly beneficial for reducing mortality and hospitalization rates. One 2016 study even found that getting a flu shot was as effective or better at preventing a heart attack than quitting smoking.