Influenza vaccine facts for kids

Influenza vaccines, often called flu shots, are special medicines that protect you from getting sick with the influenza virus, also known as the flu. The flu virus changes quickly, so new versions of the vaccine are made twice a year. These vaccines usually offer good protection against the flu. People started getting flu shots in the 1930s, and they became widely available in the United States in 1945.

Both the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC) suggest that almost everyone over six months old get a flu shot every year. This is especially important for people who are at higher risk of getting very sick. The flu vaccine is even on the WHO's list of important medicines. The European Centre for Disease Prevention and Control (ECDC) also recommends yearly shots for high-risk groups. These groups include pregnant women, older people, young children (six months to five years), and those with certain health problems.

Flu vaccines are generally safe, even for people with severe egg allergies. A common side effect is soreness where the shot was given. Some children might get a fever, and some people might feel tired or have temporary muscle aches. In a few years, the vaccine was linked to a very small increase in a condition called Guillain–Barré syndrome in older people. This happened in about one out of every million doses. If someone has had a very bad allergic reaction (like anaphylaxis) to a flu vaccine before, they should not get it again. Flu vaccines come in different forms: some use a killed virus, and others use a weakened live virus. The weakened live vaccine is usually not recommended for pregnant women, children under two, adults over 50, or people with a weak immune system. Depending on the type, the vaccine can be injected into a muscle, sprayed into the nose, or injected into the middle layer of the skin.

How Flu Vaccines Started

People have been trying to protect themselves from illnesses for a long time. During the terrible Spanish flu pandemic in 1918, doctors tried many things. They even tried giving blood from people who had recovered to those who were sick.

Scientists learned how to grow viruses in chicken eggs in 1931. This was a big step! Later, in the 1940s, the US military created the first approved flu vaccines that used killed viruses. These were used during World War II. Even today, many flu vaccines are made using chicken eggs. Scientists have also found ways to make vaccines using cell cultures or recombinant proteins, which means they use parts of the virus made in a lab.

Different Kinds of Flu Shots

There are different types of flu vaccines. Some are called "trivalent" and protect against three flu strains. Others are "quadrivalent" and protect against four strains.

In 2012, a quadrivalent flu vaccine that you could spray into your nose was approved. More quadrivalent shots became available later. Recently, scientists noticed that one type of flu virus, called B/Yamagata, might have disappeared because of the steps people took during the COVID-19 pandemic. Because of this, the World Health Organization now suggests that future flu vaccines might only need to protect against three strains instead of four.

Why Get a Flu Shot?

The US Centers for Disease Control and Prevention (CDC) says the flu vaccine is the best way to protect yourself from the flu and stop it from spreading. If you get the flu even after being vaccinated, the shot can make your sickness less severe. It takes about two weeks after your shot for your body to build up protection.

Studies show that flu shots are pretty good at preventing the flu. For example, one study found they were 67% effective overall. They seemed to help people with HIV/AIDS and healthy adults and children the most. The flu vaccine might also help protect your heart!

How Well Do Flu Shots Work?

How well a vaccine works can be measured in two ways:

• Efficacy is how well it works in perfect test conditions.
• Effectiveness is how well it works in the real world.

Flu vaccine effectiveness can change each year. This is because the flu virus changes slightly all the time, a process called antigenic drift. Even if the vaccine isn't a perfect match for the flu strains going around, it can still offer some protection.

On average, seasonal flu vaccines are about 50-60% effective at preventing flu sickness. This means some vaccinated people can still get the flu. However, getting vaccinated still helps reduce the number of people who need to go to the hospital or even die from the flu. When many school-aged children get vaccinated, it can even help protect other age groups through something called Herd immunity.

Getting a flu shot every year usually gives you good protection. Some studies suggest that getting vaccinated repeatedly might make the vaccine a little less effective for certain flu types over time, but experts still recommend getting a shot every year.

Who Should Get a Flu Shot?

The CDC recommends that everyone six months and older get a seasonal flu vaccine.

Children

The CDC suggests that children aged six months and older get the flu vaccine every year. This is especially important for children who are at high risk of getting very sick from the flu. This includes children under five years old, those with long-term illnesses, or kids with weak immune systems.

Vaccinating adults who live with or care for babies is also important. This helps reduce the chance of passing the flu to infants, who can get very sick. The flu shot seems to lower the risk of flu in children. During the 2017-18 flu season, most children who died from the flu had not been vaccinated.

Adults

For adults who don't get vaccinated, about 16% might get flu-like symptoms. For vaccinated adults, this number drops to about 10%. The vaccine can reduce confirmed flu cases.

For adults who work, the flu shot can slightly reduce flu symptoms and sick days. For healthcare workers, getting vaccinated helps protect their patients and keeps them from missing work when many people need care.

Older Adults

For adults over 65, the evidence for how well the vaccine works can be a bit unclear. Older adults are most at risk for serious flu complications, but their immune systems might not respond as strongly to the vaccine.

There are special high-dose flu vaccines made for people 65 and older. These vaccines are designed to create a stronger immune response. There's also a flu vaccine with an adjuvant (a special ingredient that helps the vaccine work better) approved for older adults.

Is the Flu Shot Safe?

Yes, flu shots are generally safe.

Side Effects

Common side effects are usually mild. You might have soreness, redness, or swelling where you got the shot. Some people get a headache, fever, feel sick to their stomach, or feel tired. Nasal spray vaccines might cause a runny nose, sore throat, cough, or wheezing.

Serious side effects, like a severe allergic reaction, are very rare. The mild, temporary side effects are much less risky than getting the flu, which can be very serious.

It's a common misunderstanding, but flu shots cannot give you the flu. The injected vaccines use killed viruses, and the nasal spray uses a very weakened virus that can't cause the flu.

Guillain–Barré Syndrome

Some people worry about a condition called Guillain–Barré syndrome (GBS) after vaccination. However, the CDC says most studies show no link between modern flu vaccines and GBS. Getting the flu itself actually increases your risk of GBS much more than the vaccine does.

Egg Allergy

Most flu vaccines are made using chicken eggs. But even if you have a severe egg allergy, flu vaccines are still recommended and are considered safe for you. Studies show that serious allergic reactions in people with egg allergies are very rare, happening in about 1.3 out of every million doses.

Newer vaccines that aren't made with eggs are also becoming available.

Other Concerns

Some flu vaccines contain a preservative called thiomersal. There has been some talk about this in the media, but the World Health Organization says there is no evidence that thiomersal in vaccines is harmful.

How Flu Vaccines Are Made

Most flu vaccines are made using fertilized chicken eggs. Here's a simplified idea of how it works:

• Scientists choose three or four flu strains they think will be common in the coming flu season.
• They inject tiny amounts of these flu viruses into chicken eggs.
• The eggs are kept warm, and the viruses grow inside them.
• After a couple of days, the liquid from the eggs is collected. This liquid contains the flu viruses.
• The viruses are then killed or weakened, and purified to make the vaccine.

Scientists are also working on a "universal" flu vaccine. This would be a single vaccine that protects against many different flu viruses, so we wouldn't need a new one every year. This is a big goal in flu research!

Flu Vaccines for Animals

Flu vaccines aren't just for humans! They are also used for animals like horses, poultry (like chickens), pigs, and dogs.

• Horses: Horses can get horse flu, which makes them sick with fever and cough. Many horse shows require horses to be vaccinated.
• Poultry: Chickens and other poultry can be vaccinated against certain types of bird flu.
• Pigs: Pig farmers use flu vaccines to protect their pigs from swine flu.
• Dogs: Dogs can get canine influenza, and there's a vaccine for that too.